hereinafter , a filament winding apparatus according to the present invention will be described in detail with reference to the accompanying drawings . first , the structure of the filament winding apparatus will be described . fig1 is a perspective view illustrating the filament winding apparatus . fig2 is a perspective view illustrating a winder portion . as shown in fig1 , the filament winding apparatus includes a winder portion 1 , and a supplier portion 2 . the winder portion 1 winds fiber bundles r onto a mandrel m . the supplier portion 2 includes creel supporters 21 , each being provided with a plurality of creels 20 . the creels 20 each hold a wound fiber bundle r . the fiber bundles r are each made up of a fiber material consisting of , for example , a glass fiber and synthetic resin . the supplier portion 2 supplies the fiber bundle r unwound from each creel 20 to the winder portion 1 . the fiber bundles r have been previously impregnated with a thermosetting synthetic resin material . note that , in some cases , the fiber bundles r are not impregnated with any resin . in such cases , a resin impregnation device ( not shown ) is provided between the winder portion 1 and the supplier portion 2 in order to apply resin to the fiber bundles r unwound from the creels 20 before they are supplied to the winder portion 1 . as shown in fig2 , the winder portion 1 includes a machine frame 10 . the machine frame 10 includes a pair of parallel first guide rails 10 a extending in its longitudinal direction 1 a . the winder portion 1 includes a mandrel holder 11 provided on the machine frame 10 . the mandrel holder 11 is capable of reciprocating along the first guide rails 10 a in the longitudinal direction 1 a . the mandrel holder 11 includes a spindle s extending in the longitudinal direction 1 a . the mandrel holder 11 rotatably supports the spindle s with spindle rotation shafts 11 a provided at its opposite ends . the spindle rotation shafts 11 a are configured to rotate the spindle s about its central axis . in the case of manufacturing a pressure tank , the mandrel m is made up of high - strength aluminum , metal , resin or the like , and shaped to have a cylindrical portion ma and domed portions mb provided at its opposite ends ( fig3 ). the spindle s removably secures the mandrel m . the mandrel m is secured to the spindle s along the central axis . accordingly , the longitudinal direction 1 a of the machine frame 10 coincides with an axial direction m 1 of the mandrel m . note that the material , shape , etc ., of the mandrel m can be changed product by product . the winder portion 1 includes a hoop winding head 12 and a helical winding head 13 . the hoop winding head 12 winds the fiber bundles r onto the mandrel m by means of hoop winding . the helical winding head 13 winds the fiber bundles r onto the mandrel m by means of helical winding . fig3 is a side view illustrating a hoop winding and helical windings . during the hoop winding , the fiber bundles r are wound roughly perpendicular to the axial direction m 1 of the mandrel m as shown in ( a ) of fig3 , whereas during the helical winding , the fiber bundles r are wound at a predetermined angle with respect to the axial direction m 1 of the mandrel m as shown in ( b ) and ( c ) of fig3 . as shown in fig2 , the winder portion 1 includes a controller portion 14 . the controller portion 14 controls the start , stop , and speed of reciprocating movement of the mandrel holder 11 , as well as the start , stop , and speed of rotation of the mandrel m via the spindle rotation shafts 11 a . furthermore , the controller portion 14 controls the start , stop , and speed of reciprocating movement of the hoop winding head 12 , as well as the start , stop , and speed of circulating movement of bobbins 12 b . as shown in fig2 , the hoop winding head 12 includes a hoop winding head body 12 a . the hoop winding head body 12 a has a passage hole 12 d disposed in its center . the hoop winding head 12 allows the mandrel m to pass therethrough via the passage hole 12 d . the machine frame 10 includes a pair of parallel second guide rails 10 b extending in the longitudinal direction 1 a . the hoop winding head body 12 a is capable of reciprocating along the second guide rails 10 b in the longitudinal direction 1 a . thus , the hoop winding head 12 can reciprocate in the longitudinal direction 1 a of the machine frame 10 , with the mandrel m passing through the passage hole 12 d . the hoop winding head 12 includes a plurality ( in the present embodiment , two ) of bobbins 12 b for holding wound fiber bundles r . the hoop winding head body 12 a has a guiding groove 12 c provided outside the passage hole 12 d along a circumferential direction m 2 of the mandrel m . the bobbins 12 b circulate along the guiding groove 12 c , so that the fiber bundles r coming out of the circulating bobbins 12 b are wound onto the mandrel m . the helical winding head 13 includes a helical winding head body 13 a . the helical winding head body 13 a has a passage hole 13 d disposed in its center . the helical winding head 13 allows the mandrel m to pass therethrough via the passage hole 13 d . the helical winding head body 13 a is secured to the machine frame 10 . reciprocating movement of the mandrel holder 11 allows the helical winding head 13 to reciprocate relatively oppositely in the longitudinal direction 1 a , with the mandrel m passing through the passage hole 13 d . the helical winding head 13 winds the fiber bundles r unwound from the supplier portion 2 onto the mandrel m . the helical winding head body 13 a has an annular guide ring portion 15 extending around the passage hole 13 d along the circumferential direction m 2 of the mandrel m . the helical winding head body 13 a has tension - creating members 13 b opposed to each other with respect to the guide ring portion 15 . the helical winding head 13 has guide rollers 13 c opposed to each other with respect to the helical winding head body 13 a . with the guide rollers 13 c , the helical winding head 13 guides the fiber bundles r unwound from the creels 20 to the tension devices 13 b . the tension devices 13 b apply predetermined tension to the fiber bundles r . the predetermined tension applied to the fiber bundles r by the tension devices 13 b allows the fiber bundles r to be securely wound onto the mandrel m . the guide ring portion 15 guides the fiber bundles r to the mandrel m . fig4 is a perspective view illustrating enlarged representations of the guide ring portion . as shown in fig4 , the guide ring portion 15 consists of a first guide ring member 150 and a second guide ring member 151 , which are shaped in the same annular form . the first guide ring member 150 and the second guide ring member 151 are in contact with each other in the longitudinal direction 1 a of the machine frame 10 ( the axial direction m 1 of the mandrel m ). the first and second guide ring members 150 and 151 have a plurality of guide holes 15 a provided along a circumferential direction 1 b of the guide ring portion 15 . the circumferential direction 1 b of the guide ring portion 15 coincides with the circumferential direction m 2 of the mandrel m . the guide holes 15 a are directed to the center of the guide ring portion 15 . the guide ring portion 15 guides the fiber bundles r to the mandrel m while passing each fiber bundle r through a corresponding one of the guide holes 15 a . the first and second guide ring members 150 and 151 have the same number of guide holes 15 a provided at regular intervals . fig5 is a front view illustrating the helical winding head 13 . as shown in fig5 , the helical winding head 13 includes a plurality of ring - like auxiliary guides 13 e . the auxiliary guides 13 e are arranged outside the guide ring portion 15 along the circumferential direction 1 b of the guide ring portion 15 . the fiber bundles r unwound from the creels 20 are supplied from opposite sides of the helical winding head 13 through the guide rollers 13 c to the tension devices 13 b . the fiber bundles r are guided from the tension devices 13 b through the auxiliary guides 13 e to the guide holes 15 a in the guide ring portion 15 . fig6 is a perspective view illustrating a bundle spreading guide . as shown in fig6 , the guide ring portion 15 has provided on its inside the bundle spreading guide 16 per guide hole 15 a . the bundle spreading guide 16 has a pair of bundle spreading rollers 16 a rotatably provided thereto . the bundle spreading rollers 16 a are provided in parallel to each other in the diametrical direction of the guide hole 15 a . the bundle spreading guide 16 includes a rotating base 16 b capable of rotating about the center of the guide hole 15 a . the rotating base 16 b supports the bundle spreading rollers 16 a . the bundle spreading guide 16 is configured to pass the fiber bundle r between the pair of bundle spreading rollers 16 a . therefore , even if the angle is changed at which to wind the fiber bundle r onto the mandrel m , the bundle spreading guide 16 can rotate to freely change its direction to wind the fiber bundle r onto the mandrel m , with the fiber bundle r being spread by the bundle spreading rollers 16 a ( i . e ., the width of the fiber bundle becomes wider ). fig7 is a diagram for describing a repositioning mechanism , in which ( a ) is an exploded perspective view of the guide ring portion , and ( b ) is a cross - sectional side view of a portion of the guide ring portion . as shown in fig7 , the guide ring portion 15 has a connection ring 152 provided around its outer circumference , such that the connection ring 152 is disposed on both the first and second guide ring members 150 and 151 to connect them together . the connection ring 152 is secured to the second guide ring member 151 . the connection ring 152 extends along the circumferential direction 1 b of the guide ring portion 15 (( a ) of fig7 ), and has a rail portion 152 a protruding toward the inside of the first guide ring member 150 (( b ) of fig7 ). the first guide ring member 150 has a guiding groove 152 b externally provided along the circumferential direction 1 b (( b ) of fig7 ). the first guide ring member 150 is secured to the helical winding head body 13 a . the rail portion 152 a of the connection ring 152 firmly attached to the second guide ring member 151 engages the guiding groove 152 b provided in the first guide ring member 150 . as a result , the second guide ring member 151 rotationally slides in the circumferential direction 1 b with respect to the first guide ring member 150 . the guide ring portion 15 includes a repositioning mechanism 17 . the repositioning mechanism 17 allows the second guide ring member 151 to rotate by a predetermined angle with respect to the first guide ring member 150 . the repositioning mechanism 17 has two semispherical concave recesses 17 a provided in a contact surface 150 a of the first guide ring member 150 that is in contact with the second guide ring member 151 . furthermore , the repositioning mechanism 17 has a ball 17 b provided in a contact face 151 a of the second guide ring member 151 that is in contact with the first guide ring member 150 , and the ball 17 b can be fitted in the recesses 17 a . the ball 17 b can emerge from / recoil into the contact face 151 a of the second guide ring member 151 in accordance with expansion / contraction of a compression spring 17 c . when the compression spring 17 c contracts , the ball 17 b recoils to allow rotation of the second guide ring member 151 . on the other hand , when the compression spring 17 c expands , the ball 17 b engages one of the recesses 17 a , so that the second guide ring member 151 is fixed in one of two shift positions , thereby allowing the guide ring portion 15 to shift between first and second states . the distance l 2 between the recesses 17 a is half the distance l 1 between two adjacent guide holes 15 a (( a ) of fig7 ). when the guide ring portion 15 is in the first state , each guide hole 15 a in the second guide ring member 151 faces an intermediary position between two adjacent guide holes 15 a in the first guide ring member 150 as shown in ( a ) of fig4 . specifically , in the circumferential direction 1 b , each center line 150 b , which theoretically extends in the diametrical direction 1 a of its one corresponding guide hole 15 a in the first guide ring member 150 ( the diametrical direction being identical to the longitudinal direction 1 a ), is equally distanced from two adjacent center lines 151 b , each theoretically extending in the diametrical direction 1 a of its one corresponding guide hole 15 a in the second guide ring member 151 . furthermore , when the guide ring portion 15 is in the second state , each guide hole 15 a of the first guide ring member 150 is aligned with one of the guide holes 15 a in the second guide ring member 151 as shown in ( b ) of fig4 . specifically , in the circumferential direction 1 b , each center line 150 b , which theoretically extends in the diametrical direction 1 a of its one corresponding guide hole 15 a in the first guide ring member 150 , overlaps with one of the center lines 151 b , each theoretically extending in the diametrical direction 1 a of its one corresponding guide hole 15 a in the second guide ring member 151 . fig8 is an enlarged side view illustrating a fiber bundle r wound by means of helical winding . as shown in fig8 , the fiber bundle r wound by means of helical winding is inclined at a predetermined angle ( winding angle ) of θ with respect to the axial direction m 1 of the mandrel m . the winding angle of θ can be changed variously in accordance with , for example , mechanical strength required by the product . here , for each fiber bundle r , if the dimension ( width ) in the direction perpendicular to a length direction r 1 is w , the dimension ( perimeter section ) in the circumferential direction m 2 of the mandrel m is a , and the winding angle is θ , the following equation ( 1 ) is established . for the mandrel m , if the radius is r , and the dimension ( entire perimeter ) in the circumferential direction m 2 is b , the following equation ( 2 ) is established . accordingly , in the case of covering the mandrel m with one layer of fiber bundles r , if the number of fiber bundles r that are to be arranged in parallel to each other without any overlap ( and space ) in the circumferential direction m 2 of the mandrel m is n , the following equation ( 3 ) can be established in accordance with the above equations ( 1 ) and ( 2 ). the helical winding head 13 is capable of covering the entire perimeter of the mandrel m with the fiber bundles r at one time . here , the term “ one time ” refers to a single operation in which the head 13 traverses the mandrel m from one end to the other as shown in fig1 . in addition , the helical winding head 13 is capable of carrying out the helical winding in two patterns respectively at winding angles of θ 1 (( b ) of fig3 ) and θ 2 (& gt ; θ 1 ) (( c ) of fig3 ). according to the above equation ( 3 ), when the winding angle is θ 1 , the number of fiber bundles r that are to be arranged in parallel to each other without any overlap ( and space ) in the circumferential direction m 2 of the mandrel m is n 1 =( 2πr · cos θ 1 )/ w . in addition , when the winding angle is θ 2 , the number of fiber bundles r is n 2 =( 2πr · cos θ 2 )/ w . note that the relationship between the above winding angles is such that θ 1 & lt ; θ 2 , and therefore the relationship between the above numbers of fiber bundles r is such that n 1 & gt ; n 2 . the guide ring portion 15 is configured as described below , such that the helical winding is carried out with the winding angle of θ 1 in the first state or with the winding angle of θ 2 in the second state . the relationship between the numbers of fiber bundles r during the helical winding is such that n 2 × 2 = n 1 . that is , the winding angles of θ 1 and θ 2 are set such that the relationship n 2 × 2 = n 1 is established . moreover , the first and second guide ring members 150 and 151 each have n 2 guide holes 15 a arranged at regular intervals . accordingly , by bringing the guide ring portion 15 into the first state , each guide hole 15 a in the guide ring member 150 is equally displaced from its one corresponding guide hole 15 a in the guide ring member 151 (( a ) of fig4 ), and therefore n 2 × 2 (= n 1 ) guide holes 15 a are considered to be arranged in the circumferential direction m 2 of the mandrel m . in addition , by bringing the guide ring portion 15 back into the second state , each guide hole 15 a in the guide ring member 150 is aligned with one of the guide holes 15 a in the guide ring member 151 (( b ) of fig4 ), and therefore n 2 pairs ( sets ) of aligned guide holes 15 a are considered to be arranged in the circumferential direction of the mandrel m . therefore , in theory , when the guide ring portion 15 is in the first state , there are n 2 × 2 (= n 1 ) guide holes 15 a arranged in the circumferential direction m 2 of the mandrel m , whereas when the guide ring portion 15 is in the second state , there are n 2 pairs of aligned guide holes 15 a arranged in the circumferential direction m 2 of the mandrel m . thus , by bringing the guide ring portion 15 into the first state , n 2 × 2 (= n 1 ) fiber bundles r are wound onto the mandrel m at one time , thereby achieving the helical winding with the winding angle of θ 1 . furthermore , by bringing the guide ring portion 15 into the second state , n 2 pairs ( sets ) of fiber bundles r are wound onto the mandrel m at one time , such that the fiber bundles r in each pair are stuck together ( to form two layers ), thereby achieving the helical winding with the winding angle of θ 2 . described next are winding operations of the filament winding apparatus . fig9 is a side view illustrating the winding operation of the filament winding apparatus during hoop winding . during the hoop winding , the hoop winding head 12 is controlled by the controller portion 14 as described below , so as to operate as shown in fig9 . first , the hoop winding head 12 is positioned at one end ( left side in the figure ; hereinafter referred to as the “ left end ”) of the cylindrical portion ma of the mandrel m (( a ) of fig9 ). thereafter , two fiber bundles r unwound from their respective bobbins 12 b are attached to the left end of the cylindrical portion ma with adhesive tape or suchlike . at this time , the two fiber bundles r are arranged in parallel to each other without leaving any space therebetween in the axial direction m 1 of the mandrel m . thereafter , the hoop winding head 12 moves toward the other end ( right side in the figure ; hereinafter , referred to as the “ right end ”) of the cylindrical portion ma , while circulating the bobbins 12 b . as a result , the two fiber bundles r are further drawn out of the bobbins 12 b . the two fiber bundles r are roughly perpendicular to ( slightly inclined from ) the axial direction m 1 of the mandrel m , and they are arranged in parallel to each other without any overlap and space therebetween . to achieve such an arrangement , the moving speed of the hoop winding head 12 and the circulating speed of the bobbins 12 b are suitably determined . by moving the hoop winding head 12 from the left end of the cylindrical portion ma (( a ) of fig9 ) to the right end (( b ) of fig9 ), one layer of fiber bundles r is formed on the cylindrical portion ma . subsequently , the hoop winding head 12 moves from the right end (( b ) of fig9 ) to the left end (( a ) of fig9 ). one reciprocation of the hoop winding head 12 results in two layers of fiber bundles r formed on the cylindrical portion ma . to carry out further winding , the above - described operation is repeated a predetermined number of times . thereafter , the fiber bundles r are cut by cutting means ( not shown ), thereby completing the hoop winding . fig1 is a side view illustrating the winding operation of the filament winding apparatus during helical winding ( with the winding angle of θ 1 ). during the helical winding ( with the winding angle of θ 1 ), the mandrel holder 11 is controlled by the controller portion 14 as described below , so as to operate as shown in fig1 . first , the helical winding head 13 is positioned at the other end ( right side in the figure ; hereinafter , referred to as the “ right end ”) of the mandrel m , i . e ., the end of the right - side domed portion mb in the figure , (( a ) of fig1 ). thereafter , the guide ring portion 15 of the helical winding head 13 is brought into the first state . in the first state , n 2 × 2 (= n 1 ) guide holes 15 a are arranged at regular intervals in the guide ring portion 15 as described above . thereafter , n 1 fiber bundles r drawn out of the guide holes 15 a are attached with adhesive tape or suchlike to the right end of the mandrel m in the circumferential direction m 2 of the mandrel m . subsequently , the mandrel holder 11 moves , so that the helical winding head 13 moves relatively in the opposite direction , from the right end of the mandrel m (( a ) of fig1 ) to the other end ( left side in the figure ; hereinafter , referred to as the “ left end ”) (( b ) of fig1 ). simultaneously with this movement , the mandrel m is rotated via the spindle rotation shafts 11 a . the n 1 fiber bundles r are wound at the winding angle of θ 1 with respect to the axial direction m 1 of the mandrel m , such that they are arranged in parallel to each other without any overlap and space therebetween . to achieve such an arrangement , the moving speed of the helical winding head 13 ( the mandrel holder 11 ) and the rotating speed of the mandrel m ( the spindle rotation shafts 11 a ) are suitably determined . by moving the helical winding head 13 from the right end (( a ) of fig1 ) to the left end (( b ) of fig1 ), one layer of fiber bundles r is formed on the mandrel m . subsequently , the helical winding head 13 moves from the left end (( b ) of fig1 ) to the right end (( a ) of fig1 ). one reciprocation of the helical winding head 13 results in two layers of fiber bundles r formed on the mandrel m . to carry out further winding , the above - described operation is repeated a predetermined number of times . thereafter , the fiber bundles r are cut by cutting means ( not shown ), thereby completing the helical winding . however , in the case of subsequently carrying out helical winding with the winding angle of θ 2 or hoop winding , the winding can be immediately carried out without cutting the fiber bundles r . specifically , in the case of subsequently carrying out the helical winding with the winding angle of θ 2 , the guide ring portion 15 is brought into the second state before carrying out an operation as described below . alternatively , in the case of subsequently carrying out the hoop winding , the hoop winding head 12 is activated , with the helical winding head 13 being positioned at the right end of the mandrel m . fig1 is a side view illustrating the winding operation of the filament winding apparatus during the helical winding ( with the winding angle of θ 2 ). during the helical winding ( with the winding angle of θ 2 ), the mandrel holder 11 is controlled by the controller portion 14 as described below , so as to operate as shown in fig1 . first , the helical winding head 13 is positioned at one end ( right side in the figure ; hereinafter , referred to as the “ right end ”) of the mandrel m , i . e ., the end of the right - side domed portion mb in the figure , (( a ) of fig1 ). thereafter , the guide ring portion 15 of the helical winding head 13 is brought into the second state . in the second state , n 2 pairs ( sets ) of guide holes 15 a are arranged at regular intervals in the guide ring portion 15 as described above . in this case , n 2 pairs of fiber bundles r are unwound from the guide holes 15 a ( where n 2 denotes the number of pairs of fiber bundles r stuck together as described above , and the number of fiber bundles r is n 2 × 2 = n 1 ). the n 2 pairs of fiber bundles r are then adhered with adhesive tape or suchlike to the right end in the circumferential direction m 2 of the mandrel m . thereafter , the mandrel holder 11 moves , so that the helical winding head 13 moves relatively in the opposite direction , from the right end (( a ) of fig1 ) to the other end ( left side in the figure ; hereinafter , referred to as the “ left end ”) (( b ) of fig1 ). simultaneously with this movement , the mandrel m is rotated via the spindle rotation shafts 11 a . the n 2 pairs of fiber bundles r are wound in parallel to each other at the winding angle of θ 2 with respect to the axial direction m 1 of the mandrel m , without any overlap and space therebetween . to achieve such an arrangement , the moving speed of the helical winding head 13 ( the mandrel holder 11 ) and the rotating speed of the mandrel m ( the spindle rotation shafts 11 a ) are suitably determined . by moving the helical winding head 13 from the right end (( a ) of fig1 ) to the left end (( b ) of fig1 ), two layers of fiber bundles r are formed on the mandrel m . specifically , the pairs of fiber bundles r , each consisting of two fiber bundles r stuck together , are wound , so that the two layers of fiber bundles r are formed at one time . subsequently , the helical winding head 13 moves from the left end (( b ) of fig1 ) to the right end , and stops there (( a ) of fig1 ). one reciprocation of the helical winding head 13 results in four layers ( two layers × 2 ) of fiber bundles r formed on the mandrel m . to carry out further winding , the above - described operation is repeated a predetermined number of times . thereafter , the fiber bundles r are cut by cutting means ( not shown ), thereby completing the helical winding . however , in the case of subsequently carrying out helical winding with the winding angle of θ 1 or hoop winding , the winding can be carried out without cutting the fiber bundles r . specifically , in the case of subsequently carrying out the helical winding with the winding angle of θ 1 , the guide ring portion 15 is brought into the first state before carrying out the above - described operation . alternatively , in the case of subsequently carrying out the hoop winding , the hoop winding head 12 is activated , with the helical winding head 13 being positioned at the right end of the mandrel m . note that the filament winding apparatus according to the present invention is not limited by the above embodiment , and can be configured as described below . three or more guide ring members may be employed to carry out the helical winding in three or more patterns . each guide array may be provided by arranging a plurality of ring - shaped guide portions . the guide portions do not have to be arranged at regular intervals . the repositioning mechanism is not limited to the above - described structure . any mechanism can be employed so long as it can change the position of one guide array relative to another along the circumference direction of the mandrel .