the following sequentially describes embodiments 1 through 19 of medical syringes of the present invention with the aid of drawings . fig1 is a cross sectional diagram showing structures of a prefilled syringe and a connector ( a locknut ) according to embodiment 1 . note that , here , a structure is adopted in which a prefilled syringe and a locknut are combined , however , the present invention may be applied to syringes other than prefilled syringes . for convenience of explanation , a plunger 40 is shown here in normal lateral view rather than in cross section . as shown in fig1 , a prefilled syringe 1 may comprise a syringe body 10 , the plunger ( also referred to as a piston ) 40 and the like . in this embodiment , the syringe body 10 is a tubular body formed by injection molding a material with high chemical resistance , such as polyethylene , polypropylene , polycarbonate or polyvinyl chloride . the tip end of the syringe body 10 is sealed by a top face portion 110 , and a luer part 120 juts or extends out from the center of the top face portion 110 . on the other hand , an opening 12 may be formed at the posterior end of the syringe body 10 . although the luer part 120 is formed by drawing to basically give a tapered shape , a stepped portion 123 is provided in a part of the tapered shape , which thereby forms a luer base portion 121 having a smaller diameter and a luer tip portion 122 located on the tip side of the luer part 120 having a larger diameter . a locknut 30 , to be hereinafter described , may be fitted to the stepped portion 123 . in addition , the luer tip portion 122 may be formed in a tapered shape in compliance with iso6 / 100 so that the regular needle hub 20 can be attached easily . in fig1 , a cap 20 is attached to the tip of the luer part 120 . in the following description , the longitudinal direction of the syringe body 10 is referred to as an “ axial direction ” while a direction perpendicular to the axial direction is referred to as a “ radial direction ”. the plunger 40 can be made of a resin material with high chemical resistance , similarly to the syringe body 10 , and includes a plunger body 42 having a cruciform cross sectional shape for the purpose of reinforcement , at each end of which are formed disk - shaped end pieces having main surfaces in the radial direction . one of the end pieces is a pressing end portion 41 to be pressed by the user with a thumb , and the other end piece is a head portion 43 that is inserted inside the syringe body 10 in the axial direction . a packing 44 is provided at the tip of the head portion 43 in a manner to make tight contact with the internal wall of the syringe body 10 . here , medication 100 is held in the syringe body 10 , which is internally sealed by the packing 44 and the cap 20 . when using the prefilled syringe 1 having such a structure , the user removes the cap 20 to enable discharge of the medication 100 . as the user pushes the pressing end portion 41 of the plunger 40 into the syringe body 10 with a thumb , the medication 100 is discharged from the tip of the luer part 120 according to the depressed amount of the plunger 40 . the prefilled syringe 1 of embodiment 1 includes the locknut 30 , which is a connector easily detachable from the luer part 120 , and which is attached so as to engage , in the axial direction , with the stepped portion 123 of the luer part 120 . the locknut 30 is used in the medical field as a connection implement for connecting the prefilled syringe 10 to a fixed connection port of a transfusion line system or blood collection line system . the locknut 30 has a cylindrical form with a bottom , being formed by injection molding a resin material with high mechanical strength . a screw thread is cut on the internal surface of a lateral side portion 301 , which corresponds to the cylindrical part of the locknut 30 , to thereby form a female screw 3010 in compliance with , for example , iso594 - 2 . the female screw 3010 may engage with a male screw 5010 to be hereinafter described . a snowman - shaped hole 3020 formed by perforating two holes communicating with each other is provided on a main surface portion 302 that is the bottom of the locknut 30 ( for detail , see fig2 ). one of these two holes is a loose - insertion hole 3021 and is formed on the main surface portion 302 away from the center by perforation . the other hole is an engaging hole 3022 which is formed in the center of the main surface portion 302 by perforation . the loose - insertion hole 3021 has a diameter at least larger than that of the luer tip portion 122 so that the entire luer part 120 of the prefilled syringe 1 can be inserted into the hole with clearance therebetween . on the other hand , the engaging hole 2022 has a diameter slightly smaller than that of the luer tip portion 122 so that the stepped portion 123 of the luer part 120 is fitted thereto and the locknut 30 rotates with respect to the luer part 120 . a passage 303 is formed between the loose - insertion hole 3021 and engaging hole 3022 , having a diameter further smaller than that of the engaging hole 3022 . the width of the passage 303 is slightly smaller than the diameter of the luer base portion 121 so that the luer part 120 shifts to the passage 303 side only when more than a certain amount of force is applied to the luer base portion 121 . fig2 a shows how to attach the locknut 30 to the syringe 1 and fig2 b shows the locknut 30 after the attachment . as to the locknut 30 having the above structure , when using the prefilled syringe 1 , the user first inserts the luer part 120 of the prefilled syringe 1 into the loose - insertion hole 3021 in the axial direction , as shown in fig2 a ( fig2 a shows that the luer part 120 is about to be inserted in the direction a , i . e . the axial direction ). since the loose - insertion hole 3021 has a diameter sufficiently larger than that of the luer tip portion 122 of the luer part 120 , the luer part 120 can be smoothly inserted into the locknut 30 . in the second step after the user has inserted the luer part 120 into the loose - insertion hole 3021 so as to assuredly insert the luer base portion 121 thereto , the user brings the lateral side of the luer base portion 121 into contact with the lateral surface of the loose - insertion hole 3021 and shifts the luer part 120 to the engaging hole 3022 via the passage 303 ( fig2 a also shows that the luer part 120 is to be shifted in the direction b ). in this process , the luer base portion 121 is forcedly shifted through the passage 303 , then the stepped portion 123 shifts and becomes fitted into the small engaging hole 3022 . since the diameter of the engaging hole 3022 matches that of the stepped portion 123 and the passage 303 exists between the engaging hole 3022 and loose - insertion hole 3021 , the stepped portion 123 of the luer part 120 abuts against the circumference of the engaging hole 3022 and is securely engaged in the axial direction , as shown in fig2 b . after the locknut 30 having the snowman - shaped hole 3020 is engaged with the syringe body 10 , these two can be readily detached from each other in the following manner . that is , the user shifts the luer part 120 from the engaging hole 3022 to the insertion hole 3021 as exerting some force on the luer part 120 . this operation can be performed in a reversible and simple fashion ( for example , in one hand ), and the user is therefore able to easily attach the locknut 30 to the prefilled syringe 1 when required , and detach the locknut 30 , when not required , to thereby use the prefilled syringe 1 alone . fig3 is a cross sectional view showing that the prefilled syringe 1 is connected , using the locknut 30 , to a fixed connection port 50 of a transfusion line system . as the male screw 5010 of the port 50 is screwed into the female screw 3010 of the locknut 30 , the luer tip portion 122 of the luer part 120 of the prefilled syringe 1 comes in close contact with a packing 52 provided inside the port 50 , and eventually gets inserted into the transfusion line while pressing the packing 52 . at this point , in the locknut 30 , the circumference of the engaging hole 3022 exerts pressure on the stepped portion 123 of the luer part 120 so that they tightly engage with each other . thus , even if some degree of tension is applied to the prefilled syringe 1 , the prefilled syringe 1 does not come apart from the port 50 along the axial direction . as a result , the user is able to safely push the plunger 40 into the syringe body 10 accordingly and deliver a required amount of medication 100 to the inside of the port 50 . on the other hand , fig4 is a cross sectional view showing that the locknut 30 has been detached from the prefilled syringe 1 , which is then connected to a direct connection port 500 of a transfusion line system . thus , according to embodiment 1 , since the locknut 30 has been taken off , or otherwise may be an obstacle , the luer tip portion 122 of the prefilled syringe 1 is properly and tightly held by the packing 52 in the port 500 , which makes a suitable connection between the prefilled syringe 1 and the port 500 . fig5 is a cross sectional view showing that the locknut 30 has been detached from the prefilled syringe 1 and a needle hub 60 is attached to the luer tip portion 122 . the needle hub 60 has a structure in which a socket portion 61 composed of a resin material and formed to match the shape of the luer tip portion 122 holds a needle tube 62 which is an injection needle . with the conventional prefilled syringe in which the locknut is fixed and cannot be detached therefrom as shown in fig4 , the locknut obstructs the view of the user and makes it difficult to determine the positioning of the luer part and the needle hub , thereby creating the danger of the user mistakenly pricking himself / herself and coming into contact with infectious material . in addition , the conventional problem that the needle hub cannot be deeply placed in and attached to the luer part due to the presence of the locknut can be fundamentally solved by embodiment 1 since the snowman - shaped hole 3020 enables easy detachment of the locknut 30 from the prefilled syringe 1 . note that although in embodiment 1 the snowman - shaped hole is formed by circular insertion and engaging holes communicating with each other via the passage , the following embodiments are also within the scope of the present invention . with a snowman - shaped hole 3020 a in a locknut 30 a of embodiment 2 shown in fig6 , arcs of a loose - insertion hole 3021 a and an engaging hole 3022 a are partially overlapped with each other , and two circumferences of these holes where they overlap form a passage 303 a . with the snowman - shaped hole 3020 a having such a shape , the present invention is able to achieve an equivalent effect to that of embodiment 1 . in addition , since the passage 303 a of embodiment 2 is formed where the loose - insertion hole 3021 a and engaging hole 3022 a overlap , it is rather edged as compared with that of embodiment 1 , and the luer part 120 is reliably engaged with the engaging hole 3022 a due to the shape . with a snowman - shaped hole 3020 b in a locknut 30 b according to embodiment 3 shown in fig7 , an engaging hole 3022 b is formed between two insertion holes 3021 b a and 3021 b b . although arcs of the engaging hole 3022 b and each of the insertion holes 3021 b a and 3021 b b are partially overlapped with each other , these holes may be communicated with each other by passages therebetween . in addition , the insertion holes 3021 b a and 3021 b b need not have the same size and shape , but need to have sizes such that at least the stepped portion 123 of the luer part 120 can be inserted thereto with clearance therebetween . with the snowman - shaped hole 3020 b having such a structure , the user can detach the locknut 30 easily when using the syringe 1 since the luer part 120 can be shifted from the engaging hole 3022 b to either of the two insertion holes 3021 b a and 3021 b b . this results in reducing the operational load on the user . embodiment 3 is expected to achieve a very high level of convenience especially in medical practices which require the user to handle the prefilled syringe 1 and locknut 30 in one hand based on the treatment method using the prefilled syringe 1 . with a snowman - shaped hole 3020 c in a locknut 30 c of embodiment 4 shown in fig8 , a circular engaging hole 3022 c is communicated with a rectangular loose - insertion hole 3021 c via a passage 3023 c . with such a structure also , a similar effect to that of the locknut 30 of embodiment 1 can be achieved . an additional advantage is that the user readily recognizes and distinguishes the loose - insertion hole 3021 c and engaging hole 3022 c without confusion and is able to properly use the locknut 30 c since the shapes of these holes are distinctly different . with a snowman - shaped hole 3020 d in a locknut 30 d of embodiment 5 shown in fig9 , a circular engaging hole 3022 d is communicated with a hexagonal loose - insertion hole 3021 d via a passage 3023 d . with such a structure also , a similar effect to that of the locknut 30 of embodiment 1 can be achieved . similarly to embodiment 4 , since the shapes of the loose - insertion hole 3021 d and engaging hole 3022 d are distinctly different , the user readily recognizes and distinguishes these two holes without confusion and is able to properly use the locknut 30 d . although the prefilled syringe 1 of the present invention has been explained with an example in which the needle hub 60 is attached after the locknut 30 being detached , the present invention is not limited to that case . instead of a needle hub , a tubelike luer or a tube may be used . it is effective to attach , from the top , a cap or the like to the prefilled syringe 1 with a needle hub attached thereto so as to protectively cover the needle hub and needle tube for the purpose of avoiding accidental pricking . as such a cap , one similar to a cap for a vial container can be used . each embodiment described above discloses a structural example of a connector ( locknut ) in which a screw thread is cut to form a female screw . however , the present invention is not confined to this structure , and the prefilled syringe 1 may be appropriately connected to the port of a line system using a discontinuous thread , a cup joint , or another structure . the luer part of the syringe used in the present invention does not necessarily have a circular cross section , and either one of the luer tip portion and the luer base portion or both have rectangular , elliptic , or triangle cross sections . note however that it is preferable that the shape of the engaging hole be appropriately decided in accordance with the cross sectional shape of the stepped portion of the luer part so as to stably and reliably engage the luer part in the engaging hole of the locknut . fig1 is a cross sectional view showing structures of a prefilled syringe and a connector ( locknut ) according to embodiment 1 . note that embodiment 6 has a structure in which a prefilled syringe and a locknut are combined , however , the present invention is applicable to syringes other than prefilled syringes . for convenience of explanation , the plunger 40 is shown here in normal lateral view rather than in cross section . the prefilled syringe 1 shown in the figure may comprise the syringe body 10 , the plunger ( also referred to as a piston ) 40 and the like . the syringe body 10 may be a tubular body formed by injection molding a material with high chemical resistance , such as polyethylene , polypropylene , polycarbonate or polyvinyl chloride . the tip end of the syringe body 10 is sealed by the top face portion 110 , and the luer part 120 formed by drawing to give a tapered shape juts or extends out from the center of the top face portion 110 . the luer part 120 is formed in a tapered shape in compliance with is06 / 100 so that the normal needle hub 20 is easily attached thereto . in fig1 , the cap 20 is attached to the tip of the luer part 120 . the prefilled syringe 1 of the present invention is configured , such that convex portions 101 and 102 and a concave portion 103 are provided side by side , situated closer to the luer part 120 , so as to encircle the circumference of the syringe body 10 . these portions are for engaging with the locknut 30 to be hereinafter described . on the other hand , the opening 12 is formed at the posterior end of the syringe body 10 . in the following description , the longitudinal direction of the syringe body 10 is referred to as an “ axial direction ” while a direction perpendicular to the axial direction is referred to as a “ radial direction ”. the plunger 40 is made of a resin material with high chemical resistance , similarly to the syringe body 10 , and includes the plunger body 42 having a cruciform cross sectional shape for the purpose of reinforcement , at each end of which are formed disk - shaped end pieces having main surfaces in the radial direction . one of the end pieces is the pressing end portion 41 to be pressed by the user with a thumb , and the other end piece is the head portion 43 that is inserted inside the syringe body 10 in the axial direction . the packing 44 is provided at the tip of the head portion 43 in a manner to make tight contact with the internal wall of the syringe body 10 . here , medication 100 is held in the syringe body 10 , which is internally sealed by the packing 44 and the cap 20 . when using the prefilled syringe 1 having such a structure , the user removes the cap 20 to enable discharge of the medication 100 . as the user pushes the pressing end portion 41 of the plunger 40 into the syringe body 10 with a thumb , the medication 100 is discharged from the tip of the luer part 120 according to the depressed amount of the plunger . the prefilled syringe 1 of embodiment 6 is configured , such that the locknut 30 , which is a connector easily detachable from the luer part 120 , is attached thereto as shown in fig1 . the locknut 30 is used in the medical field as a connection implement for connecting the prefilled syringe 10 to a fixed connection port of a transfusion line system or blood collection line system . the locknut 30 has a cylindrical shape having a bottom , and is formed by injection molding a resin material with high mechanical strength . a screw thread is cut on the internal surface of a lateral side portion 301 , which corresponds to the cylindrical part of the locknut 30 , to thereby form a female screw 3010 in compliance with , for example , iso594 - 2 . the female screw 3010 engages with the male screw 5010 to be hereinafter described . a rib 3020 having in the center a perforation with a size such that the luer part 120 can be inserted , leaving no space therebetween , is formed in the locknut 30 , and forms a bulkhead which divides the internal space of the locknut 30 into a syringe side and a port side . on the other hand , outside the locknut 30 , two plate - like arms 31 and 32 are formed parallel to the syringe body 10 in the axial direction to make t shapes with the rib . tab projections 310 and 320 having triangular cross sections are formed on the inner sides of the tip ends of the arms 31 and 32 . the shape of the projections 310 and 320 is made to be complementary to that of the concave portion 103 of the syringe body 10 . fig1 shows the way of engaging the locknut 30 and the state of locknut 30 after the engagement . as to the locknut 30 having the above structure , when the prefilled syringe 1 is used , the user first inserts the luer part 120 into the locknut 30 ( here , the luer part 120 is inserted in the center of the rib 3020 inside the locknut 30 ) as shown in fig1 . at this point , the user makes sure that the luer part 120 is inserted so that the rib 3020 comes all the way to the base of the luer part 120 . in the second step , using the arms 31 and 32 extending from the locknut 30 , the user engages the projections 310 and 320 provided on the inner sides of the arms 31 and 32 with the concave portion 103 of the syringe body 10 by elastically contacting and fitting them with each other . the shape of the projection 310 and 320 is formed so as to conform to the convex portions 101 and 102 and the concave portion 103 , and therefore the locknut 30 is securely kept on the syringe body 10 by the engagement . fig1 is a cross sectional view showing the prefilled syringe 1 that is , using the locknut 30 , connected to the fixed connection port 50 of a transfusion line system . as the male screw 5010 of the port 50 is screwed into the female screw 3010 of the locknut 30 , the tip of the luer part 120 of the prefilled syringe 1 is tightly pressing the packing 52 provided inside the port 50 , and eventually gets inserted into the transfusion line . the prefilled syringe 1 is not disengaged while in use because the syringe body 10 is securely fixed with the locknut 30 by the convex portions 101 and 102 , concave portion 103 , and projections 310 and 320 , and besides the luer part 120 is supported by the rib 3020 in the locknut 30 to keep the luer part 120 in place . as a result , the user is able to safely push the plunger 40 into the syringe body 10 accordingly and deliver a required amount of medication 100 to the inside of the port 50 . according to embodiment 6 , after being engaged with the syringe body 10 , the locknut 30 can be easily disengaged from the syringe 1 by performing a predetermined operation in the following manner . this operation can be performed in a reversible and simple fashion ( for example , in one hand ), and the user is therefore able to easily engage the locknut 30 with the prefilled syringe 1 when required , and detach the locknut 30 , when not required , to thereby use the prefilled syringe 1 alone . in a specific method of disengaging the locknut 30 ( the predetermined operation ), the user presses the arms 31 and 32 on the anterior side of the syringe 1 , as shown in fig1 , which is a cross sectional view of the syringe 1 and locknut 30 . in this embodiment , “ the principle of leverage ” may be applied , with the centers of the arms 31 and 32 being fulcrums while the points where the projections 310 and 320 abut on the convex portions 101 being working points . accordingly , the ends of the arms 31 and 32 where the projections 310 and 320 are provided warp away from the syringe body 10 ( i . e . an external force is applied to the locknut 30 in a direction different from the syringe axial direction ). herewith , the projections 310 and 320 detach and come free , at least , from the convex portion 102 and concave portion 103 . while maintaining this state , the user is able to pull out the locknut 30 from the syringe 1 with a little force . note that the locknut 30 can be easily disengaged from the syringe body 10 by spreading outward the ends of the arms 31 and 32 with the projections 310 and 320 by fingers , instead of pressing the arms 31 and 32 on the anterior side of the syringe 1 . it is desirable that the arms 31 and 32 be provided on the locknut 30 so that t shapes are formed with the rib , and points where the arms 31 and 32 abut on the rib become fulcrums . this , the user can easily disengage the locknut 30 from the syringe body 10 by pushing the posterior ends of the arms 31 and 32 to spread the anterior ends thereof . fig1 is a cross sectional view showing that the prefilled syringe 1 may be connected to the direct connection port 500 of a transfusion line system after the locknut 30 has been detached therefrom according to the above method . thus , in embodiment 6 , since the locknut 30 has been removed , or may otherwise be an obstacle , the luer part 120 of the prefilled syringe 1 is properly and tightly held by the packing 52 in the port 500 , which makes a suitable connection between the prefilled syringe 1 and the port 500 . fig1 is a cross sectional view showing that the needle hub 70 is attached to the luer part 120 after the locknut 30 has been detached from the prefilled syringe 1 . the needle hub 70 has a structure in which a socket portion 71 composed of a resin material and formed to match the shape of the luer part 120 holds a needle tube 72 which is an injection needle . with the conventional prefilled syringe in which the locknut is fixed and cannot be detached therefrom as shown in fig4 , the locknut obstructs the view of the user and makes it difficult to check on the positioning of the luer and the needle hub , thereby creating the danger of the user mistakenly pricking himself / herself and coming into contact with infectious material . in addition , the conventional problem that the needle hub cannot be deeply placed in and attached to the luer part due to the presence of the locknut can be fundamentally solved by embodiment 6 since the user can readily detach the locknut 30 from the prefilled syringe 1 by handling the arms 31 and 32 in a simple fashion . note that embodiment 6 has a structure in which one projection 310 or 320 having a triangular cross section is formed on the end of each arm 31 and 32 and fitted with the convex portions 101 and 102 and concave portion 103 of the syringe body 10 . however , the following embodiments are also within the scope of the present invention . as to embodiment 7 shown in fig1 , although the structure of the locknut 30 is substantially similar to that of embodiment 1 , the syringe body 10 has a slightly different structure . embodiment 7 is characterized by a male screw portion 104 formed with a helical convex portion provided on the outer surface of the syringe body 10 . with using the syringe body 10 having the male screw portion 104 also , the present invention is able to achieve an equivalent effect to that of embodiment 6 . in addition , embodiment 7 allows for a slight adjustment of the positional relationship between the syringe body 10 and the locknut 30 by changing the degree of screwing of the male screw portion 104 into the locknut 30 ( i . e . how far the male screw portion 104 is screwed into the locknut 30 ). consequently , embodiment 7 achieves a good connection of the syringe 1 to a fixed connection port corresponding to the luer part 120 shorter than a conventional one . as to embodiment 8 shown in fig1 , although the structure of the locknut 30 is substantially similar to that of embodiment 6 , the syringe body 10 has a slightly different structure . embodiment 8 is configured to have a concave portion 105 which is formed by concaving the outer surface of the syringe body 10 . with using the syringe body 10 having the concave portion 105 also , embodiment 8 is able to achieve an equivalent effect to that of embodiment 6 . in addition , since the syringe body 10 of embodiment 8 has a smooth surface without the convex portions 101 and 102 , a problem such as the convex portions 101 and 102 of the syringe body 10 catching the user &# 39 ; s clothes while in use can be avoided . it is a matter of course that the syringe body 10 according to embodiment 8 must have enough thickness for the formation of the concave portion 105 . as to embodiment 9 shown in fig1 , although the structure of the syringe body 10 is substantially similar to that of embodiment 6 , a locknut 35 has a slightly different structure . embodiment 9 is characterized by projection sets 351 and 352 , each of which includes multiple projections , formed on the inner sides of the tip ends of arms 36 and 37 , respectively . here , in the respective sets 351 and 352 , the projections are provided with a predetermined distance therebetween . with using the syringe body 10 having the locknut 35 also , embodiment 9 is able to achieve an equivalent effect to that of embodiment 6 . especially since the multiple projections of the sets 351 and 352 are fitted with the syringe body 10 , embodiment 9 allows for a more reliable fixation of the syringe 1 and locknut 35 . although the prefilled syringe 1 of the present invention has been explained with an example in which the needle hub 60 is attached after the locknut 30 being detached , the present invention is not limited to that case . instead of a needle hub , a tubelike luer or a tube may be used . it is effective to attach , from the top , a cap or the like to the prefilled syringe 1 with a needle hub attached thereto so as to protectively cover the needle hub and needle tube for the purpose of avoiding accidental pricking . as such a cap , one similar to a cap for a vial container can be used . each embodiment described above discloses a structural example of a locknut having a female screw formed therein . however , the present invention is not confined to this structure , and the prefilled syringe 1 may be appropriately connected to the port of a line system using a discontinuous thread , a cup joint , or another structure . in addition , although each embodiment above describes a structural example of a locknut having two arms , the present invention is not limited to the number of arms . further more , instead of the arms , a tubular extension may be formed by extending the cylindrical body of the locknut in the axial direction , and projections may be provided on the inner side of the extension . in this case , it is desirable that the locknut and syringe be engaged with each other by not fitting engagement , but screwing engagement in view of the elastic deformation properties of the locknut . the luer part of the syringe used in the present invention does not necessarily have a circular cross section , and may have a rectangular , elliptic or triangle cross section , for example . note however that , in this case , a port and a needle hub matching the shape of the luer part have to be employed . in addition , the present invention may have a structure in which multiple arms are provided that extend from the outer circumference of the top face portion positioned at the base of the luer part , and are engaged with the convex portion formed on the outer surface of the locknut . in this case , the structure is designed so that each arm is detached from the locknut by applying external forces to the syringe body in a direction different from the axial direction . fig1 is a cross sectional diagram showing structures of a prefilled syringe and a connector ( locknut ) according to embodiment 10 . for convenience of explanation , the plunger 40 is shown here in normal lateral view rather than in cross section . the prefilled syringe 1 shown in fig1 may comprise the syringe body 10 , the plunger ( also referred to as a piston ) 40 and the like . the syringe body 10 may be a tubular body formed by injection molding a material with high chemical resistance , such as polyethylene , polypropylene , polycarbonate or polyvinyl chloride . the tip end of the syringe body 10 is sealed by the top face portion 110 , and the luer part 120 juts out from the center of the top face portion 110 . on the other hand , the opening 12 is formed at the posterior end of the syringe body 10 . although the luer part 120 is formed by drawing to basically give a tapered shape , the stepped portion 123 is provided in a part of the tapered shape , which thereby forms the luer base portion 121 having a smaller diameter and the luer tip portion 122 located on the tip side of the luer part 120 and having a larger diameter . a fixture 20 , to be hereinafter described , is fitted to the stepped portion 123 . in addition , the luer tip portion 122 is formed in a tapered shape in compliance with iso6 / 100 so that the regular needle hub 20 can be attached thereto easily . in fig1 , the cap 15 is attached to the tip of the luer part 120 . in the following description , the longitudinal direction of the syringe body 10 is referred to as an “ axial direction ” while a direction perpendicular to the axial direction is referred to as a “ radial direction ”. the plunger 40 is made of a resin material with high chemical resistance , similarly to the syringe body 10 , and includes the plunger body 42 having a cruciform cross sectional shape for the purpose of reinforcement , at each end of which are formed disk - shaped end pieces having main surfaces in the radial direction . one of the end pieces is the pressing end portion 41 to be pressed by the user with a thumb , and the other end piece is the head portion 43 that is inserted inside the syringe body 10 in the axial direction . the packing 44 is provided at the tip of the head portion 43 in a manner to make tight contact with the internal wall of the syringe body 10 . here , medication 100 is held in the syringe body 10 , which is internally sealed by the packing 44 and the cap 20 . when using the prefilled syringe 1 having such a structure , the user removes the cap 20 to enable discharge of the medication 100 . as the user pushes the pressing end portion of the plunger 40 into the syringe body 10 with a thumb , the medication 100 is discharged from the tip of the luer part 120 according to the depressed amount of the plunger . the prefilled syringe 1 of embodiment 10 is constructed such that the locknut 30 , which is a connector easily detachable from the syringe body 10 , is inserted onto the luer part 120 in the axial direction and attached thereto so as to be engaged with the fixture 20 positioned at the stepped portion 123 . the locknut 30 is used in the medical field as a connection implement for connecting the prefilled syringe 10 to a fixed connection port of a transfusion line system or blood collection line system . note that , here , the prefilled syringe 1 is adopted as a syringe for engaging with the locknut 30 ; however , the present invention may be applied to syringes other than prefilled syringes . the fixture 20 is formed by injection molding a resin material with mechanical strength and appropriate elasticity . as shown in the assembly drawing of fig2 , the fixture 20 comprises : a platy fixture body 201 having an insertion hole 202 ; two platy arms 205 and 206 extending in one direction from the periphery of the fixture body 201 ; and two platy levers 203 and 204 also extending in the opposite direction from the periphery of the fixture body 201 . the diameter of the insertion hole 202 of the fixture body 201 is slightly smaller than that of the luer tip portion 122 of the luer part 120 , but larger than that of the luer base portion 121 . the fixture 20 is inserted onto the luer part 120 through the insertion hole 202 and then forcedly shifted to fit at the luer base portion , and whereby the stepped portion 123 abuts on the periphery of the insertion hole 202 and the fixture 20 is held so as to be not easily separated from the luer part 120 . in order to favorably hold the fixture body 201 by “ forced fit ” at the stepped portion 123 using the insertion hole 202 , it is desirable to make the insertion hole 202 have the minimum possible diameter that enables the luer base portion 121 to pass therethrough . in addition , the diameter enabling the “ forced fit ” varies according to the elasticity of the material of the fixture body 201 , and therefore it is desirable to take into account the size of the luer base portion 121 and the material properties of the fixture 20 for designing the insertion hole 202 . the two arms 205 and 206 extend in the syringe axial direction , and projections 2050 and 2060 , each having a triangular cross section , are formed inside the tip ends of the arms 205 and 206 . note that the cross - sectional shape of the projections 2050 and 2060 may be rectangular , semicircular , or other forms . the two levers 203 and 204 and the arms 205 and 206 are formed swayable so that each of these sets warps away from the syringe axis , with portions thereof adjacent to the fixture body 201 being fixed points and their tip ends spreading like open tweezers . as shown in fig2 , the levers 203 and 204 are formed to be symmetric with the two arms 205 and 206 , respectively , around the fixed points of the fixture 201 , and thereby when the levers 203 and 204 are pressed , the arms 205 and 206 open up , warping away from the syringe axis . this mechanism is for detaching the locknut 30 . note that it is desirable to use a material having appropriate elasticity ( polypropylene , for example ) for the fixture 20 in order to favorably design the insertion hole 202 and achieve the swayable mechanism . the locknut 30 has a cylindrical shape having a bottom , and is formed by injection molding a resin material with high mechanical strength . a screw thread is cut on the internal surface of the lateral side portion ( outer surface ) 301 , which corresponds to the cylindrical part of the locknut 30 , to thereby form the female screw 3010 in compliance with , for example , iso594 - 2 . the female screw 3010 engages with the male screw to be hereinafter described . an insertion hole 305 is provided on the main surface portion 302 that is the bottom of the locknut 30 . the insertion hole 305 is formed to have a diameter at least larger than that of the luer tip portion 122 so that the entire luer part 120 of the prefilled syringe 1 is inserted thereto with clearance therebetween . concave portions 303 and 304 are formed on the lateral side portion 301 of the locknut . these concave portions 303 and 304 have , for example , a rectangular cross section , and their locations and sizes are determined so that the concave portions 303 and 304 can engage with the projections 2050 and 2060 provided on the arms 205 and 206 of the fixture 20 . as a characteristic of embodiment 10 , the engagement of the syringe body 10 and locknut 30 using the fixture 20 is described with reference to the assembly drawing of fig2 . note that fig2 shows an operation of attaching the fixture 20 to the luer part 120 , and this operation takes place only when the fixture 20 is attached to the syringe body 10 for the first time . once the luer part 120 and fixture 20 are attached to each other , the present invention does not require to detach them again . as to the locknut 30 having the above structure and the fixture 20 fitted with the luer base portion 121 of the luer part 120 and held at the stepped portion 123 , the user first presses the levers 203 and 204 by gripping them with fingers so as to open the tip ends of the arms 205 and 206 away from the axial direction , as shown in fig2 . while this state is maintained , the user inserts , into the insertion hole 305 along the axial direction , the luer tip portion 122 of the luer part 120 to which the fixture 20 is attached . at this point , since the insertion hole 305 has a sufficiently large diameter as compared to the luer tip portion 122 of the luer part 120 , the user can smoothly insert the luer part 120 into the locknut 30 . note that the size of the insertion hole 305 may be set so that the insertion hole 305 is slidable over the luer tip portion 122 to some degree , and then a device preventing the locknut 30 from easily disengaging from the luer tip portion 122 may be provided . after shifting the locknut 30 sufficiently to the luer part 120 side , as the second step , the user checks on the relative positions of the concave portions 303 and 304 provided on the locknut &# 39 ; s lateral side portion 301 and the projections 2050 and 2060 of the fixture 20 , and releases the pressure applied on the levers 203 and 204 . herewith , the projections 2050 and 2060 of the arms 205 and 206 engage with the concave portions 303 and 304 of the locknut 30 , and whereby the locknut 30 is favorably held on the syringe body 10 by means of the fixture 20 . on the other hand , the fixture 20 and locknut 30 can , after being engaged with each other , be again detached by performing a predetermined operation ( i . e . applying an external force on the fixture 20 in a direction different from the syringe axial direction ) in the following manner . that is , when the user presses the levers 203 and 204 while grasping the fixture 20 , the projections 2050 and 2060 of the arms 205 and 206 are released from the concave portions 303 and 304 of the locknut 30 according to so - called “ the principle of leverage ”, and in this state of things , the user can pull the locknut 30 out along the axial direction . this operation can be performed in a reversible and simple fashion ( for example , in one hand ), and the user is therefore able to easily attach the locknut 30 to the prefilled syringe 1 when required , and detach the locknut 30 , when not required , to thereby use the prefilled syringe 1 alone . fig2 is a cross sectional view showing that the prefilled syringe 1 may be connected , using the locknut 30 , to the fixed connection port 50 of a transfusion line system . the male screw of the port 50 is screwed into the female screw 3010 of the locknut 30 shown in fig2 , and herewith the luer tip portion 122 of the luer part 120 of the prefilled syringe 1 is in close contact with the packing 52 provided inside the port 50 and is inserted into the transfusion line . the locknut 30 is tightly engaged with the syringe 1 by the projections 2050 and 2060 of the arms 205 and 206 and the concave portions 303 and 304 of the locknut 30 so that the prefilled syringe 1 does not come apart from the port 50 along the axial direction even if some degree of tension is applied to the prefilled syringe 1 . as a result , the user is able to leave the prefilled syringe 1 connected to the port 50 over a long period of time and deliver a required amount of medication 100 to the inside of the port 50 by safely pushing the plunger 40 into the syringe body 10 . on the other hand , fig2 is a cross sectional view showing that the prefilled syringe 1 is connected to the direct connection port 500 of a transfusion line system after the locknut 30 has been detached from the prefilled syringe 1 . with the prefilled syringe 1 from which the locknut 30 has been detached , no obstacle exists around the luer tip portion . it is therefore possible to , without the interference of the locknut 30 , achieve a suitable connection between the prefilled syringe 1 and the port 500 by properly and tightly holding the luer tip portion 122 with the packing 52 in the port 500 . as a result , with the direct connection port 500 also , the user is able to leave the prefilled syringe 1 connected to the port 500 over a long period of time and deliver a required amount of medication 100 to the inside of the port 50 by safely pushing the plunger 40 into the syringe body 10 . fig2 is a cross sectional view showing that the needle hub 60 is attached to the luer tip portion 122 after the locknut 30 has been detached from the prefilled syringe 1 . the needle hub 60 has a structure in which the socket portion 61 composed of a resin material and formed to match the shape of the luer tip portion 122 holds the needle tube 62 which is an injection needle . with the conventional prefilled syringe in which the locknut is fixed and cannot be detached therefrom as shown in fig4 , the locknut obstructs the view of the user and makes it difficult to visually determine the positioning of the luer and the needle hub , thereby creating the danger of the user mistakenly pricking himself / herself and coming into contact with infectious material . however , embodiment 1 solves such a conventional problem since allowing for easy observation of the positional relationship around the luer between the levers 205 and 206 which spread like open tweezers from the fixture 20 . note that although in embodiment 10 the locknut 30 is attached to the syringe using the arms 205 and 206 and concave portions 303 and 304 , the following embodiments are also within the scope of the present invention . in a structural example of embodiment 11 shown in fig2 , slit - shaped concave portions 303 e and 304 e are formed on a lateral side portion 301 e of a locknut 30 e along the circumference thereof . on the other hand , in addition to levers 203 a and 204 a similar to the levers 203 and 204 of embodiment 10 , arms 205 a and 206 a are provided , each shaped like an arc of a semicircle in cross section . these arms 205 a and 206 a extend from a fixture body 20 a , and a slit 207 a is created on the arms 205 a and 206 a adjacent to the boundary between the arms 205 a and 206 a and the fixture body 201 a . with the slit 207 a , the arms 205 a and 206 a spread like open tweezers when the user presses the levers 203 a and 204 a . on the inner side of the tip ends of the arms 205 a and 206 a , projections 2050 a and 2060 a are formed to match the shape of the slit - shaped concave portions 303 e and 304 e . embodiment 11 with the fixture 20 and locknut 30 having such structures can achieve an equivalent effect to that of embodiment 10 . in addition , embodiment 11 has a structure in which the arms 205 a and 206 a hold the locknut 30 e in a manner to encase it , enabling more reliably attachment of the locknut 30 e to the syringe 1 without any play . furthermore , according to embodiment 11 , even if torque is applied to the locknut 30 e in the radial direction while in use , the engagement of the slit - shaped concave portions 303 e and 304 e and the projections 2050 a and 2060 a favorably prevents the locknut 30 a from rotating , which results in maintaining stable engagement of the syringe 1 and locknut 30 e . in a structural example of embodiment 12 shown in fig2 , a female screw portion 303 b is spirally formed on a lateral side portion 301 b of the locknut 30 b along the circumference thereof . on the other hand , in addition to levers 203 b and 204 b similar to the levers 203 and 204 of embodiment 10 , arms 205 b and 206 b having male screw portions 2050 b and 2060 b made up of multiple projections are provided . the female screw portion 303 b and male screw portions 2050 b and 2060 b are formed so that they can be screwed with each other . the arms 205 b and 206 b are provided so as to extend from a fixture body 201 b , and spread like open tweezers when the user presses levers 203 b and 204 b . to attach a fixture 20 b to the locknut 30 b , the user spreads the male screw portions 2050 b and 2060 b by pressing the levers 203 b and 204 b , and brings the male screw portions 2050 b and 2060 b into contact with the female screw portion 303 b provided on the external peripheral surface of the locknut 30 b . subsequently , the male screw portions 2050 b and 2060 b and the female screw portion 303 b are screwed with each other by causing relative rotation between the fixture 20 b and locknut 30 b . embodiment 12 with the fixture 20 b and locknut 30 b having such structures can achieve an equivalent effect to that of embodiment 10 . in addition , according to embodiment 12 , it is possible to securely attach the locknut 30 b to the syringe 1 while preventing play and unwanted rotation between the fixture 20 b and locknut 30 b by adjusting the degree of screwing of the male screw portions 2050 b and 2060 b into the female screw portion 303 b ( i . e . how tightly they are locked together ). as a result , even if unwanted torque is applied to the locknut 30 b in the radial direction while in use , the engagement of the screw portions favorably prevents the locknut 30 b from rotating , which results in maintaining stable engagement of the syringe 1 and locknut 30 b . although the prefilled syringe 1 of the above embodiments has been explained with an example in which the needle hub 60 is attached after the locknut 30 being detached , the present invention is not limited to that case . instead of a needle hub , a tubelike luer or a tube may be used . it is effective to attach , from the top , a cap or the like to the prefilled syringe 1 with a needle hub attached thereto so as to protectively cover the needle hub and needle tube for the purpose of avoiding accidental pricking . as such a cap , one similar to a cap for a vial container can be used . the luer part of the syringe used in the present invention does not necessarily have a circular cross section , and either one of the luer tip portion and the luer base portion or both have rectangular , elliptic , or triangle cross sections . in brief , the luer tip portion must have a larger diameter than the luer base portion . the following describes a structure of a connecter 1 j which is a connector of embodiment 13 , with reference to fig2 . the connector 1 j is used to fixedly hold a syringe 5 j , to be hereinafter described , on a port 61 j ( see fig2 ). as shown in fig2 a , the connector 1 j is made up of : a connector body 10 j as the main body thereof ; and a locknut 20 j functioning as a constraint portion which constrains the shape of the connector body 10 j . fig2 a shows that , in the connecter 1 j , the connector body 10 j is free from the construction of the locknut 20 j . of the components of the connector 1 j , the connector body 10 j is substantially tubular with a bottom , and includes a port connecting portion 11 j and a syringe connecting portion 12 j which are integrally formed . the port connecting portion 11 j is located on the opening side of the substantially tubular connector body 10 j , and a male screw 11 a for connecting with an instrument is formed on the internal surface of the tubular body . in addition , knurling with straight ridges and grooves is provided on the outer surface of the tubular body so as to prevent slippage in an operation of connecting the connector 1 j to an instrument . the syringe connecting portion 12 j is positioned , within the connector body 10 j , at the bottom face thereof and part of the lateral wall adjacent to the bottom face . the bottom - face part of the syringe connecting portion 12 j is divided by a slit 13 j into two , up and down halves — an upper bottom member 121 j and a lower bottom member 122 j — in the y direction in the figure . the halved bottom members 121 j and 122 j are structured so that the slit 13 j therebetween is opened and closed according to the constraint force exerted by the locknut 20 j onto the connector body 10 j . a single female screw 12 a discontinued by the slit 13 j is formed on the outer surface of the syringe connecting portion 12 j . as shown in fig2 b , the upper and lower bottom members 121 j and 122 j divided by the slit 13 j into up and down halves in the y direction respectively have a petal - like shape , and swing in the y direction in the figure when no constraint force is exerted by the locknut 20 j . formed on the respective bottom members 121 j and 122 j are semicircular cutouts 121 h and 122 h . the chords of the cutouts 121 h and 122 h correspond to the lines extending from the edges of the bottom members 121 j and 122 j exposed to the slit 13 j . in the state shown in fig2 b , the cutouts 121 h and 122 h oppose each other across a space , forming an oval shape . here , a hypothetical inscribed circle 12 h of the cutouts 121 h and 122 h has a diameter of φd 0 . referring back to fig2 a , the locknut 20 j is placed to encircle the periphery of the syringe connecting portion 12 j in the connector body 10 j , and a male screw 21 j is provided on the internal peripheral surface as shown in the closeup in the figure . the male screw 21 j is to be screwed with the female screw 12 a formed on the outer surface of the syringe connecting portion 12 j in the connector body 10 j . in addition , on the outer peripheral surface of the locknut 20 j , knurling , similar to the one provided on the outer surface of the port connecting portion 11 , is performed on the outer peripheral surface of the locknut 20 j to thereby prevent slippage . when the locknut 20 j is positioned , in the x direction , to the right of the syringe connecting portion 12 j as shown in fig2 , the syringe connecting portion 12 j spreads like open tweezers toward the bottom side . herewith , the cutouts 121 h and 122 h form an oval shape as described above . the following describes a state - changeable mechanism of the connector 1 j having the above - mentioned structure . in fig2 a , the locknut 20 j is located , in the x direction , on the rightmost side of the syringe connecting portion 12 j in the connector body 10 j . in this configuration , the locknut 20 j does not apply constraint force to the syringe connecting portion 12 j . when the locknut 20 j in the configuration shown in fig2 a is shifted , in the x direction , to the left of the syringe connecting portion 12 j as being screwed into the female screw 12 a , the syringe connecting portion 12 j becomes subject to constraint force exerted by the locknut 20 j in the direction that the slit 13 j becomes narrowed — i . e . in the direction that the space between the petal shaped bottom members 121 j and 122 j becomes narrowed . when the locknut 20 j has been shifted to the vicinity of the bottom , the shape of the syringe connecting portion 12 j that previously spread like open tweezers has been transformed to be substantially tubular . with the transformation , the space between the cutouts 121 h and 122 h narrows , and the diameter of the inscribed circle 12 h is also reduced to less than the diameter φd 0 . it is preferable that the connector body 10 j be made of a material having elastic properties ( e . g . a resin material ) in consideration for repetitive attachment and detachment . although the syringe connecting portion 12 j changes its shape under the constraint force of the locknut 20 j , the transformation is performed within the elastic range of the material constituting the connector body 10 j . accordingly , the syringe connection portion 12 j returns to the state shown in fig2 a and 27b without any deformation once the constraint force of the locknut 20 j is removed . thus , the connector 1 j has a mechanism that the space between the cutouts 121 h and 122 h on the bottom members 121 j and 122 j widens and narrows simply by tightening and loosening the locknut 20 j . this mechanism is reversible and can be operated repeatedly . the general structure of a syringe 5 j is described with reference to fig2 . the syringe 5 j , part of which is shown in fig2 a , is a prefilled syringe , and a luer part 51 j juts or extends out at the right - hand end of a syringe body 52 j . formed on the base side of the luer part 51 j is a neck portion 53 j having a reduced diameter . although no illustration is given , the syringe 5 j includes a plunger , a packing and the like , and the tubular part of the syringe body 52 j is filled with the liquid medication . among the components of the syringe 5 j , the luer part 51 j has a tapered shape and a maximum outer diameter of φd 1 . the outer diameter φd 1 is smaller than the diameter d 0 of the inscribed circle 12 h of the connector 1 j in the open state shown in fig2 , i . e . ( φd 1 & lt ; φd 0 ). the neck portion 53 j on the base side of the luer part 51 j is tubular with a diameter smaller than the diameter φd 1 . a step is made in a part of the luer part 51 j close to the neck portion 53 j so as to form an engaging portion 51 a . the connection of the above - mentioned syringe 5 j and connector 1 j are described next also with reference to fig2 . as shown in fig2 a , the locknut 20 j of the connector 1 j is set back , within the syringe connecting portion 12 j , to the side closest to the port connecting portion 11 j , and whereby the connector body 10 j is kept free from the constraint force of the locknut 20 j in the radial direction , similar to the case of fig2 . the luer part 51 j of the syringe 5 j is inserted toward the inscribed circle 12 h ( not shown in fig2 ) of the cutouts 121 h and 122 h of the connector 1 j in this state ( arrow b ). here , the maximum outer diameter d 1 of the luer part 51 j and the diameter φd 0 of the inscribed circle 12 h satisfy φd 1 & lt ; φd 0 , which thereby allows for smooth insertion of the luer part 51 j . the insertion of the luer part 51 j into the connector 1 j is done when the neck portion 53 j reaches an inner bottom surface 123 j of the connector 1 j . while the center of the syringe 5 j in the radial direction is substantially aligned with that of the connector 1 j , the locknut 20 j of the connector 1 j is rotated along the female screw 12 a and shifted to the left in the figure . the shifting is done when the locknut 20 j substantially reaches the left end of the connector body 10 j . the female screw 12 a on the outer surface of the syringe connection portion 12 j is formed up to the bottom members 121 j and 122 j ( see fig1 ) so that the locknut 20 j stops thereat . as shown in fig2 b , in a condition where the locknut 20 j has been shifted to the leftmost side of the syringe connection portion 12 j , the syringe connection portion 12 j that previously spread like open tweezers as in fig2 a closes under the constraint force exerted by the locknut 20 j to be substantially tubular . with the transformation , the space between the cutouts 121 h and 122 h narrows , and the diameter of the inscribed circle 12 h is also reduced . then , the inscribed circle 12 h formed by the cutouts 121 h and 122 h becomes substantially circular in the state of fig2 b . at this point , the diameter of the inscribed circle 12 h of the connector 1 is φd 2 . the relationship between the diameters φd 1 and φd 2 is φd 2 & lt ; φd 1 . namely , in the state of fig2 b , the inner bottom surface 123 j of the connector 1 j is engaged with the engaging portion 51 a of the syringe 5 j , and the syringe 5 j is fixedly held by the connector 1 j . note that , in fig2 b , the diameter φd 2 of the open hole formed by the cutouts 121 h and 122 h in the connector 1 j is slightly larger than the outer diameter of the neck portion 53 j of the syringe 5 j so as to have a clearance therebetween . however , this clearance is not necessarily provided . as has been described , the connector 1 j is structured to be freely attachable to and detachable from the syringe 5 j by simply handling the locknut 20 j . here , the connector 1 j may be provided to the user as an accessory of the syringe 5 j , or separately by itself . in order to change a state of the syringe 5 j from one in which the connector 1 j is attached , as shown in fig2 b , to one in which the connector 1 j is detached , as shown in fig2 a , a reverse process of the above - mentioned procedure for connecting the connector 1 j may be performed . referring to fig2 , the following describes a method of connecting the syringe 5 j , to which the connector 1 j is attached , to a port of a medical instrument in the luer - lock style . in fig2 , an extension tube 6 j with a port attached thereto is used as an example of a connection target to which the syringe 5 j is connected in the luer - lock style . the extension tube 6 j of the connection target includes the port 61 j provided at one end of a tube 62 j , as shown in fig2 . within the port 61 j , a female screw 61 a is formed on the outer surface of the tubular body . the female screw 61 a corresponds to the male screw 11 a ( not shown in fig2 ; refer to fig2 and 28 ) of the connector 1 j ( i . e . the male screw 11 a can be screwed into the female screw 61 a ). on the end face of the port 61 j , a hole 63 j is provided in the central region . this hole 63 j is connected to the inner duct of the tube 62 j . the inner diameter of the hole 63 j is set slightly smaller than the maximum outer diameter φd 1 of the luer part 51 j of the syringe 5 j , and a portion of the luer part 51 j of the syringe 5 j can enter the inner duct through the hole 63 j when the syringe 5 j is connected to the extension tube 6 j . for connecting the syringe 5 j and the extension tube 6 j to each other , the user brings the connector 1 j attached to the proximity of the luer part 51 j of the syringe 5 j ( see fig2 ) forward ( arrow e ) with respect to the extension tube 6 j , and when the connector 1 j and the port 61 of the extension tube 6 j make contacts , the user starts rotating the connector 1 j in the direction of arrow c . herewith , the male screw 11 a provided in the connector body 10 j ( see fig2 and 28 ) is progressively screwed into the female screw 61 a on the port 61 j of the extension tube 6 j . at this point , the luer part 51 j of the syringe 5 j is being inserted into the hole 63 j of the extension tube 6 j . the male screw 11 a is continuously screwed into the female screw 61 a until the space between the external peripheral surface of the luer part 51 j and the periphery of the hole 63 j is closed . in the above manner , the luer - lock connection of the syringe 5 j and extension tube 6 j is completed . since the connection in the luer - lock style is stable , the syringe 5 j and the extension tube 6 j are less likely to come disengaged or loose from each other over a long period of time . referring to fig3 , the following describes a method of connecting the syringe 5 j to a port of a medical instrument in the luer - slip style . in fig3 , a coinfusion port 7 j and an injection needle 8 j are used as examples of connection targets to which the syringe 5 j is connected . for the connection in the luer - slip style , the syringe 5 j to which the connector 1 j is not attached is used , as shown in fig3 . as to the syringe 5 j , the user may use one to which no connector is originally attached , or alternatively obtain one with the connector 1 j attached thereto and use this syringe after detaching the connector 1 j therefrom . the connector 1 j can be readily detached according to a reverse process of the above - mentioned procedure shown in fig2 . for the connection in the luer - slip style , the luer part 51 j of the syringe 5 j is simply inserted into a port of a connection - target medical instrument . for example , the connection of the syringe 5 j to the coinfusion port 7 j is completed simply by inserting the luer part 51 j of the syringe 5 j into a valve plug ( not shown ) provided in a cover body 71 j . herewith , the interior of the syringe 5 j and the interior of the tubes 72 j and 73 j of the coinfusion port 7 j are communicated to each other . the valve plug of the coinfusion port 7 j is an elastic thin film , and a slit to receive the luer part 51 j is formed in a part of the valve plug . since such matters are public knowledge , the descriptions are omitted here . next , for connecting the syringe 5 j and the injection needle 8 j to each other , a needle hub 82 j of the injection needle 8 j is mounted on the luer part 51 j of the syringe 5 j . the syringe 5 j and the injection needle 8 j are connected to each other when an internal peripheral surface 82 f of the needle hub 82 j becomes tightly attached to the external peripheral surface 51 f of the luer part 51 j . although no graphic representation is given , the needle tube 81 j juts out also inside the needle hub 82 j , and the jutted part is inserted into an inner hole of the luer part 51 j when the syringe 5 j and the injection needle 8 j are connected to each other . the needle hub 82 j and the inner hole of the luer part 51 j are tightly fitted to each other while the injection needle 8 j being connected to the syringe 5 j . that is , the needle hub 81 j and the inner hole are designed so that the liquid medication will not leak out therefrom or bacteria will not enter therefrom . the luer - slip connection of the syringe 5 j and another medical instrument has been described by presenting two examples above . the syringe 5 j of fig3 does not have the connector 1 j attached thereto , allowing for quick luer - slip connection . although , there are various medical instruments that can be connected to the syringe 5 j in the luer - slip style besides the above two examples , the connection operations for those instruments are the same as above . advantages of connector 1 j and syringe 5 j having connector 1 j attached thereto as has been described above and also shown in fig2 , the connector 1 j of embodiment 13 is attachable to and detachable from the syringe 5 j by simply performing the screwing operation of the locknut 20 j . thus , in the medical practices , the user is able to readily attach and detach the connector 1 j to / from the syringe 5 j according to need . thus , since being able to attach and detach the connector 1 j functioning as a connector to / from the syringe 5 j if necessary , the user can use the detached connector 1 j with another syringe . this results in a reduction in the cost burden on the user and allows for an excellent operational performance of the syringe 5 . furthermore , the syringe 5 j can be connected to the port of another medical instrument in either the luer - slip or luer - lock style . when connecting the injection needle 8 j to the syringe 5 j , the user can use the syringe 5 j from which the connector 1 j has been detached , as shown in fig3 . thus , the syringe 5 j is also effective in preventing the user from mistakenly pricking himself / herself . note that the connector 1 j , which functions as a connector , does not have to be provided with every syringe 5 j when supplied to the user , and may be singularly provided to the user instead . in such a case , the user may attach / detach the connector 1 j to / from the syringe 5 j according to need . thus , the connector 1 j can be attached and detached , according to the connection style of the syringe 5 j with the port , at the stages of treatment and medical care in the medical practices . as a result , operating efficiency can be improved , and the number of syringe types required to be prepared in advance can be reduced . although embodiment 13 is described with an example in which the connector body 10 j is fitted to the extension tube 6 j by screwing the locknut 20 j into the connector body 10 j and thereby making the locknut 20 j shift toward the connector body 10 j , the present invention is not limited to the case . the same effect as that of embodiment 13 can be achieved , for example , with a connector having , instead of the locknut 20 j , a ring body with no screw provided on the internal peripheral surface thereof . here , the connector body 10 j is fitted to the extension tube 6 j by sliding the ring body toward the connector body 10 j . note that , in the case of adopting such a sliding mechanism , it is required to implement a measure that prevents the ring body from shifting back to the original position when the connector body 10 j is fitted to the extension tube 6 j . fixing the ring body with a pin is an example of such a measure . although , in the above embodiment , the connection target is the ( prefilled ) syringe 5 j filled with liquid medication in advance , the above operation remains the same even if a different type of syringe , other than a prefilled syringe , is used . the structure of a connector 1 k of embodiment 14 which functions as a connector is described with the aid of fig3 . as shown in fig3 a , the connector 1 k may be made up of three components : split frames 11 k and 12 k ; and a coupling portion 13 k coupling the sides of the split frames 11 k and 12 k . these three components are integrally formed . of them , the split frames 11 k and 12 k have a shape as if created by halving , along the axis , a hollow cylinder having a bottom . fig3 a and 31b show the state where the split frames 11 k and 12 k are open ( hereinafter , “ the open position ”). each of the split frames 11 k and 12 k having a shape as if created by halving a cylinder hollow having a bottom includes a semicylindrical portion 112 k / 122 k and a semicircular bottom portion 11 k / 121 k . formed on the semicylindrical portions 112 k and 122 k are sets of tabs 11 m and 12 m to be interlocked with each other . that is , the tabs 11 m and 12 m function as coupling members of the split frames 11 k and 12 k , and become interlocked with each other when the split frames 11 k and 12 k are coupled . these tabs 11 m and 12 m are designed so that , when once they are interlocked with each other , the coupling will not be disconnected unless an operation of pulling the tabs 12 m outward is performed . cutouts 11 h and 12 h are formed on the bottom portions 111 k and 112 k that butt against each other when the split frames 11 k and 12 k are engaged using the tabs 11 m and 12 m ( hereinafter , “ the closed position ”). each of the cutouts 11 h and 12 h has the shape of a semicircle with a chord coinciding with the halving line of the split frames 11 k and 12 k . furthermore , male screw portions 11 n and 12 n are provided on the inner surface of the semicylindrical portions 112 k and 122 k of the split frames 11 k and 12 k . these male screw portions 11 n and 12 n form a single , unbroken male screw when the split frames 11 k and 12 k are in the closed position . the wall thickness of the coupling portion 13 k is thinner than that of the individual split frames 11 k and 12 k , and the coupling portion 13 k will not be dismembered after repetitive opening and closing of the split frames 11 k and 12 k . the opening - and - closing mechanism of the connector 1 k having the above structure is described next with the aid of fig3 b showing the connector 1 k of fig3 a viewed from arrow a . as shown in fig3 b , in an anterior view , each of the split frames 11 k and 12 k is semicircular . when folded at the coupling portion 13 , the split frames 11 k and 12 k face to each other , and the tabs 11 m and 12 m interlock with each other . thus , the connector 1 k is substantially in the shape of a cylinder having a bottom when the tabs 11 m and 12 m engage with each other ( i . e . in the closed position ). thus , when the split frames 11 k and 12 k are joined together , the cutouts 11 h and 12 h provided on the split frames 11 k and 12 k also face to each other to form a circular hole with a diameter of φd 1 . note that the split frames 11 k and 12 k and the coupling portion 13 k , all of which are integrally formed , are preferably made of , for example , a resin material in order to achieve the above - mentioned functions . a general structure of a syringe 5 k is described with the aid of fig3 . the syringe 5 k , a part of which is shown in fig3 , is a prefilled syringe , and a luer part 51 k juts out at the right - hand end of a syringe body 52 k . formed on the base side of the luer part 51 k is a neck portion 53 k having a reduced diameter . although no illustration is given , the syringe 5 k includes a plunger , a packing and the like , and the tubular part of the syringe body 52 k is filled with the liquid medication . among the components of the syringe 5 k , the luer part 51 k has a tapered shape and a maximum outer diameter of φd 3 . the outer diameter φd 3 is larger than the diameter φd 1 of the hole formed by the cutouts 11 h and 12 h in fig3 ( i . e . φd 3 & gt ; φd 1 ). the neck portion 53 k located on the base side of the luer part 51 k is in the shape of a cylinder with an outer diameter of φd 2 . a step is made in a part of the luer part 51 k close to the neck portion 53 k so as to form an engaging portion 51 n . the connection of the above - mentioned syringe 5 k and connector 1 k is described next with reference to fig3 and 32 . the luer part 51 k of the syringe 5 k is inserted into the connector 1 k in the open position as shown in fig3 a and positioned in a manner that the neck portion 53 k sets in the edge of either the cutout 11 h or 12 h . at this point , the syringe 5 k and the connector 1 k are maintained so that their axes substantially coincide with each other . next , while the syringe 5 k is held not to move with respect to the connector 1 k , the split frames 11 k and 12 k are folded at the coupling portion 13 k so that the openings of the split frames 11 k and 12 k face to each other . the connector 1 k has the shape of a cylinder having a bottom when the tabs 11 m and 12 m of the split frames 11 k and 12 k interlock with each other . at this point , the cutouts 11 h and 12 h form a circular hole with an inner diameter of φd 1 . the syringe 5 k is thus engaged , at the neck portion 53 k , with the connector 1 k in the closed position . that is , the maximum outer diameter φd 3 of the luer part 51 k is larger than the inner diameter φd 1 of the hole formed by the cutouts 11 h and 12 h , and the engaging portion 51 n of the luer part 51 k is fixedly held by inner bottom faces 111 n and 121 n of the connector 1 k . thus , the syringe 5 k and the connector 1 k are connected to each other . the tabs 11 m / 12 m of each set are provided at two locations on the split frame 11 k / 12 k , and when these tabs 11 m and 12 m once interlock with each other , the connector 1 k does not return to the open position unless the disengagement operation ( releasing the coupling of the tabs 11 m and 12 m ) is conducted . note that the male screw portions 11 n and 12 n , each provided on the split frame 11 k / 12 k of the connector 1 k , are designed to form one unbroken male screw across a line of junction 1 kl of the split frames 11 k and 12 k . referring to fig3 , the following describes a method of connecting the syringe 5 k , to which the connector 1 k is attached , to a port of another medical instrument in the luer - lock style . in fig3 , an extension tube 6 k with a port attached thereto is used as an example of a connection target to which the syringe 5 k is connected . the extension tube 6 k being a connection target includes a port 61 k provided at one end of a tube 62 k , as shown in fig3 . within the port 61 k , a female screw portion 61 n is formed on the outer surface of the tubular body . the female screw portion 61 n corresponds to the male screw portions 11 n and 12 n of the connector 1 k . although no illustration is given , a hole is provided in the central region of the end face of the port 61 k , and functions as an opening of the inner duct of the tube 62 k . the hole in the central region of the port 61 k has an inner diameter slightly smaller than the maximum outer diameter φd 3 of the luer part 51 k of the syringe 5 k . thus , the hole of the port 61 k is designed so that the luer part 51 k of the syringe 5 k can be inserted thereinto . for connecting the syringe 5 k and the extension tube 6 k to each other , the user brings the connector 1 k attached to the syringe 5 k forward ( arrow b ) with respect to the port 61 k of the extension tube 6 k . when the connector 1 k and the port 61 k of the extension tube 6 k make contacts , the user starts rotating the connector 1 k in the direction of arrow c and still brings the connector 1 k forward . herewith , the male screw portions 11 n and 12 n provided in the split frames 11 k and 12 k are progressively screwed into the female screw portion 61 n on the port 61 k of the extension tube 6 k . in parallel with the screwing operation , the luer part 51 k of the syringe 5 k is gradually inserted into the hole on the end face of the port 61 k of the extension tube 6 k . subsequently , when the male screw portions 11 n and 12 n of the connector 1 k are completely screwed into the female screw portion 61 n of the port 61 k , the syringe 5 k and the extension tube 6 k are connected to each other . since the connection of the syringe 5 k and the extension tube 6 k with the connector 1 k therebetween ( the luer - lock connection ) is stable , the syringe 5 k and the extension tube 6 k are less likely to disengage or loose from each other over a long period of time . referring to fig3 , the following describes a method of connecting the syringe 5 k and another medical instrument in the luer - slip style . in fig3 , a coinfusion port 7 k and an injection needle 8 k are used as examples of connection targets to which the syringe 5 k is connected . for the connection in the luer - slip style , the syringe 5 k to which the connector 1 k is not attached is used , as shown in fig3 . as to the syringe 5 k , the user may use a syringe to which no connector is originally attached , or alternatively obtain a syringe with the connector 1 k attached and use this after detaching the connector 1 k therefrom . the connector 1 k can be readily detached by releasing the coupling of the interlocking tabs 11 m and 12 m . in the connection in the luer - slip style , the luer part 51 k of the syringe 5 k is simply inserted into a port of a connection - target medical instrument . for example , the connection of the syringe 5 k to the coinfusion port 7 k is completed simply by inserting the luer part 51 k of the syringe 5 k into a valve plug ( not shown ) provided in a cover body 71 k . herewith , the interior of the syringe 5 k and the interior of the tubes 72 k and 73 k of the coinfusion port 7 k are communicated to each other . the valve plug of the coinfusion port 7 k is an elastic thin film , and a slit to receive the luer part 51 k is formed in a part of the valve plug . since such matters are public knowledge , the descriptions are omitted here . next , for connecting the syringe 5 k and the injection needle 8 k to each other , a needle hub 82 k of the injection needle 8 k is mounted on the luer part 51 k of the syringe 5 k . the syringe 5 k and the injection needle 8 k are connected to each other when an internal peripheral surface 82 f of the needle hub 82 k becomes tightly attached to the external peripheral surface 51 f of the luer part 51 k . although no graphic representation is given , the needle tube 81 k juts out also inside the needle hub 82 k , and the jutted part is inserted into an inner hole of the luer part 51 k when the syringe 5 k and the injection needle 8 k are connected to each other . the needle hub 82 k and the inner hole of the luer part 51 k are tightly fitted to each other while the injection needle 8 k being connected to the syringe 5 k . that is , the needle hub 81 k and the inner hole are designed so that the liquid medication will not leak out therefrom or bacteria will not enter therefrom . the luer - slip connection of the syringe 5 k and another medical instrument has been described by presenting two examples above . the syringe 5 k of fig3 does not have the connector 1 k attached thereto , allowing for quick luer - slip connection . although there are various medical instruments can be connected to the syringe 5 k in the luer - slip style besides the above two examples , the connection operations for those instruments are the same as above . advantages of connector 1 k and syringe 5 k having connector 1 k attached thereto as has been described above and also shown in fig3 , the connector 1 k of embodiment 14 is composed of the split frames 11 k and 12 k and the coupling portion 13 k , and allows for easy attachment to the syringe 5 k by the coupling operation of the two split frames 11 k and 12 k as well as easy detachment from the syringe 5 k by releasing the interlocking tabs 11 m and 12 m and opening the split frames 11 k and 12 k . on the other hand , unless the interlocking tabs 11 m and 12 m are released , an incident in which the split frames 11 k and 12 k open up during the use of the syringe 5 k or the like is avoided . thus , since the user is able to attach and detach the connector 1 k to / from the syringe 5 k as the need arises , the connector 1 k has advantageous effects of ( 1 ) reducing the cost burden on the user , ( 2 ) not causing hindrance to the work performance when the syringe 5 k is used , and ( 3 ) enabling connection of the syringe 5 k to the port of another instrument in either the luer - slip or luer - lock style . the syringe 5 k having the connector 1 k attached thereto also exhibits these advantages . when connecting the injection needle 8 k to the syringe 5 k , the user can use the syringe 5 k from which the connector 1 k has been detached , as shown in fig3 . thus , the syringe 5 k is also effective in preventing the user from mistakenly pricking himself / herself . note that the connector 1 k does not have to be provided with every syringe 5 k when supplied to the user , and may be singularly provided to the user instead . in such a case , the user may attach / detach the connector 1 k to / from the syringe 5 k according to need . if using the syringe 5 k having the connector 1 k attached thereto for treatment and testing in the medical practices , the user is able to select whether to attach or detach the connector 1 k according to the connection style of the syringe to the port . thus , using the syringe 5 k with the connector 1 k attached thereto achieves high efficiency in the medical practices . a connector 2 of embodiment 15 is described with the aid of fig3 . the connector 2 k is composed of split frames 21 k and 22 k as shown in fig3 , and differs from the connector 1 k in that these split frames 21 k and 22 k are separated from each other . that is , the connector 2 k can be said to be the connector 1 k of embodiment 14 from which the coupling portion 13 k is removed . note however that the connector 2 has additional tabs 11 m and 12 m formed on the split frames 21 k and 22 k at the locations corresponding to where the coupling portion 13 k is attached . since other components of the connector 2 k are the same as those of the connector 1 k , the descriptions are omitted here . attachment of the connector 2 k to the syringe 5 k is achieved by setting the neck portion 53 k of the syringe 5 in the cutouts 21 h and 22 h while the split frames 21 k and 22 k are separated from each other , and then interlocking the tabs 11 m of the split frame 21 k and the tabs 12 m of the split frame 22 k . here , the relationships of the inner diameter of the hole formed by the cutouts 21 h and 22 h with the maximum outer diameter of the luer part 51 k of the syringe 5 k , and with the outer diameter of the neck portion 53 k are the same as those of connector 1 k of embodiment 14 above . the connector 2 k is easily detached from the syringe 5 k by doing the reverse of the above procedure , i . e . releasing the interlocking tabs 11 m and 12 m . accordingly , also when using the connector 2 k according to the present embodiment , the user is able to easily attach and detach the connector 2 k to / from the syringe 5 k as the need arises . as a result , the connector 2 k of embodiment 15 also has advantageous effects of ( 1 ) reducing the cost burden on the user , ( 2 ) not causing hindrance to the work performance when the syringe 5 k is used , and ( 3 ) enabling connection of the syringe 5 k to the port of another instrument in either the luer - slip or luer - lock style . a connector 3 k of embodiment 16 is described next with the aid of fig3 . the connector 3 k is characterized by the split balance of split frames 31 k and 32 k different from that of split frames 11 k and 12 k of the connector 1 k , as shown in fig3 . that is , while the split frames 11 k and 12 k of the connector 1 k have a shape as if they were formed by halving , along the axis , a hollow cylinder with a bottom , the split frame 32 k of the connector 3 k according to the present embodiment has a shape as if it was formed by halving only the bottom face and the vicinity thereof of a hollow cylinder with a bottom . the opening and closing of the connector 3 k is basically the same as that of the connector 1 k shown in fig3 . besides the advantageous effects of the connector 1 k , the connector 3 k has an additional advantage of having a cylindrical part which exhibits higher stiffness when the connector 3 k is being screwed on another medical instrument ( e . g . the extension tube 6 k of fig3 ), as compared to that of the connector 1 k . that is , when a male screw 31 n of the connector 3 k is screwed into the female screw of the medical instrument to thereby join the connector 3 k with the medical instrument , the cylindrical part of the connector 3 k receives a force also in the outer radial direction . at this point , the connector 3 k whose cylindrical part is not split has an advantage in exhibiting higher stiffness in the radial direction than the connector 1 k whose cylindrical part is split . this means that the connector 3 k enables to set the syringe more firmly on the port of another medical instrument . in embodiments 14 to 16 above , the features , functions and effects of the present invention are described by taking as examples three kinds of connectors 1 k , 2 k and 3 k , however , the present invention is not limited to those . although , in embodiment 14 above , a prefilled syringe filled with liquid medication in advance is used as an example of the syringe , the above - mentioned functions and effects remain the same even if a syringe of a different type is used . in embodiments 14 to 16 , the connector 1 k , 2 k or 3 k is connected to the syringe 5 k by using the neck portion 53 k formed on the base side of the luer part 51 k of the syringe 5 k . however , it is not necessary that the neck portion 53 k is formed on the base side of the luer part 51 k . for example , similar functions and effects to the above can be achieved by providing a narrowed part ( which corresponds to the neck portion ) on a part of the external peripheral surface of the syringe body 52 k and forming a connector to correspond to the narrowed part . fig3 a , 36 b , 36 c and 36 d illustrate a structure of a syringe of embodiment 17 . a syringe 100 l is a prefilled syringe filled with liquid medication 110 l in advance , and allows for speedy insertion and removal into / out of either the luer - lock coinfusion port or the luer - slip coinfusion port . regarding the syringe 100 , as shown in fig3 a , a cylindrical syringe portion 120 l is filled with the liquid medication 110 l and subsequently sealed by a plunger portion 150 l , and a lock part 130 l ( which is an example of a connection supporting member ) is freely rotatably coupled to one end of the syringe portion 120 l by means of a coupling pin 160 l ( which is an example of a pin ). in the syringe part 120 l , a cylindrical luer part 140 l extends from one end ( hereinafter referred to as “ the first end ”) of a cylindrical syringe body 121 l , and a flange 121 a is provided at the opposite end to the first end ( hereinafter referred to as “ the second end ”). the luer part 140 l is cylindrical , and may be composed of : a 1 st luer portion 144 l with a diameter d 1 on the base side ; and a tapered 2 nd luer portion 141 l located on the tip side of the luer part 140 l and having a tip - end diameter d 2 and a rear - end diameter d 3 . with this arrangement , d 3 & gt ; d 2 and d 3 & gt ; d 1 . the lock part 130 l is made of a resin material , and is a cylindrical nut with a bottom for engaging the syringe 100 l and a connection - target instrument . a through hole 134 l of a diameter d 4 is provided on the bottom face of the lock part 130 l , and through holes 132 a and 132 b with rectangular openings are provided on the lateral side of the cylindrical body . note that d 4 is larger than d 3 to enable the 2 nd luer portion 141 l to pass through the through hole 134 l . the coupling pin 160 l is a substantially u - shaped pin for engaging the lock part 130 l and the luer part 140 l , and has a function of engaging with the 1 st luer portion 144 l while penetrating through the hull of the lock part 130 l to be thereby fitted with the lock part 130 l . to be more specific , as shown in fig3 d which is a cutaway view of the coupling pin 160 l fitted with the lock part 130 l and cut parallel to the main surface thereof , the coupling pin 160 l is a substantially u - shaped pin having two symmetric extending portions 163 l extending from a rectangular base portion 161 l . stepped portions 162 l , which abut against the lock part 130 l when inserted thereinto , are provided at the base of the extending portions 163 l , and a projecting portion 163 a is provided on the outer side of each extending portion 163 l , towards the tip end thereof . provided in the center of the groove 164 l formed between these two extending portions 163 l is a concave portion 165 l to which the 1st luer portion 144 l is fitted . there is no problem whether the lock part 130 l and coupling pin 160 l are detached or attached from / to the syringe 100 l when the syringe 100 l is delivered to a medical practice site . here , for convenience of explanation , the syringe 100 l is used from which the lock part 130 l and coupling pin 160 l have been detached at the time of delivery . the following explains how to use the syringe 100 l . when a coinfusion port to which the syringe 100 l is to be connected is a luer - lock coinfusion port , a person ( hereinafter , the “ operator ”) inserts the luer part 140 l into the through hole 134 l of the lock part 130 l , as shown in fig3 a . subsequently , the operator inserts the coupling pin 160 l into the through holes 132 a and 132 b of the lock part 130 l as shown in fig3 b , and pushes the coupling pin 160 l thereinto until the edges of the stepped portions 162 l of the lock part 130 l make contacts with edges 162 a of both sides of the through hole 132 a , as shown in fig3 a to 37f . at this point , the projecting portions 163 a of the coupling pin 160 l go over contact points 162 b on both sides of the through hole 132 b and thereby prohibit the coupling pins 160 l from shifting in the reverse direction of the insertion . at the same time , the 1 st luer portion 144 l is fitted into the concave portion 165 l . here , the 1st luer portion 144 l and the lock part 130 l are engaged with each other to be positioned concentrically . in addition , since the contact faces of the 1st luer portion 144 l and the concave portion 165 l of the coupling pin 160 l slip against each other in the circumferential direction , the 1st luer portion 144 l and the lock part 130 l rotate relatively to each other around the central axis of the 1st luer portion 144 l . as to the above - mentioned coinfusion port 200 l which is a luer - lock coinfusion port , on the lateral side of a port body 201 l functioning as a transfusion line or a similar flow path , a rubber valve 204 having a hole 204 a is held in place by being covered with a cylindrical cover body 202 l . a screw thread is cut on the external periphery of the cover body 202 l to thereby form a thread groove 203 l . when connecting the syringe 100 l to the coinfusion port 200 l , the operator rotates the lock part 130 l and screws the lock part 130 l onto the thread groove 203 l while inserting the 2nd luer portion 141 l of the syringe 100 l into the hole 204 a of the coinfusion port 200 l , as shown in fig3 c , and whereby the syringe 100 l is securely connected to the coinfusion port 200 l . when connecting the syringe 100 l to the luer - slip coinfusion port 210 l , the operator is able to rapidly connect the syringe 100 l , to which the lock part 130 l is not attached , to a coinfusion port 210 l by inserting the 2nd luer portion 141 l into the hole 204 a of the coinfusion port 210 l , as shown in fig3 . thus , since the syringe 100 l of the present embodiment allows for easy attachment and detachment of the lock part 130 l by insertion and pullout of the coupling pin 160 l , the syringe 100 l is smoothly connected to a luer - slip style instrument by detaching the lock part 130 l from the syringe 100 l , similarly to the case of a conventional luer - slip syringe . when the syringe 100 l is connected to an instrument in the luer - lock style , secure connection can be established by attaching the lock part 130 l to the syringe 100 l , similarly to the case of a conventional luer - lock syringe . in embodiment 17 , the 1 st luer portion 144 l and the lock part 130 l are designed to rotate relatively to each other , however , the present invention is not limited to this . for example , the following structure may be employed : a spline parallel to the syringe axis direction ( hereinafter , “ the 1 st spline ) is provided on the outer surface of the 1 st luer portion 144 l of the syringe 100 l , and another spline ( hereinafter , “ the 2 nd spline ”) corresponding to the 1 st spline is provided on the concave portion 165 l of the coupling pin 160 l . herewith , when the 1 st luer portion 144 l is fitted into the concave portion 165 l , the 1 st and 2 nd splines are fitted with each other so that the 1 st luer portion 144 l is positionally fixed in relation to the concave portion 165 l . in this case , although the syringe 100 l and the lock part 130 l cannot rotate relative to each other , the above - mentioned nut can be screwed by rotating the entire syringe 100 l while inserting the 2 nd luer portion 141 l into a target location since the lock part 130 l and the 1 st luer portion 144 l are in a concentric configuration . note also that , although in embodiment 17 the lock part 130 l of the syringe 100 l is a nut that engages with an instrument such as a coinfusion port , this is merely an example and the part does not have to be a nut . for instance , as in embodiment 18 shown in fig3 , a lock part 132 l having claw portions 133 a and 133 b may be used instead of the lock part 130 l having a thread . in this case , the change in the locking mechanism of the syringe necessitates a change in the structure of the engaging portion of the luer - lock coinfusion port . a coinfusion port 220 l having two l - shaped grooves 231 a is one example of such a structural change . note that , although the coupling pin 160 l is substantially u - shaped , this is merely an example . if a pin fulfills a similar function , i . e . enabling the lock part 130 l and the luer part 140 l to be fixed at a determined position , the pin may take any shape . for example , a coupling pin 180 of embodiment 19 shown in fig4 ( corresponding to fig3 d ) may be used . here , a lock part 170 l has been formed by partially revising the cross - sectional shape of the lock part 130 l so that the lock part 170 l serves the function fulfilled by one of the two extending portions 163 l of the coupling pin 160 l , and the coupling pin 180 l has only one extending portion 163 l . the connector - attached syringes , connectors used for syringes , and syringes of the present invention can be used to apply liquid medication to patients and collect blood in medical practices . the connector - attached syringes and connectors of the present invention are adaptable for both luer - slip and luer - lock style ports , providing a cost reduction to the users . the present invention is applicable to manufacturing medical syringes used in medical practices in which various types of connection ports are used .
the present invention aims at offering : a syringe connectable to a port in a fixed manner as well as capable of demonstrating high operational performance even in the case of direct connection where a connector is not used ; a connector used for the syringe ; and a syringe able to attach the connector thereto . for the attainment of the above objectives , the medical syringe of the present invention is a medical syringe including a cylindrical connection supporting member which enhances the holding force of a luer part inserted into a port when the medical syringe is connected to the port . the connection supporting member is set by sliding along the luer or a syringe body in a state of being movable between a first position near a tip of the luer and a second position away from the tip of the luer . the medical syringe is characterized in that , when the connection supporting member is moved to the second position , the tip of the luer part is exposed .