now , this invention will be discussed in detail in conjunction with one preferred embodiment thereof with reference to the accompanying drawings . fig2 is a front perspective view of a blindstitch machine of this invention , and fig3 is a partial front perspective view showing the internal structure of the machine . in these drawings , 1a is a head in which a driving system of a needle 3 , a driving system of a feed dog 5 , etc . are contained , 1b is an arm incorporating a main shaft 2 which transmits the driving force of a motor ( not shown ) received by a pulley 9 to the driving system , etc ., and 1c represents a bed provided with a driving system of a pair of belts 7a , 7a , and the like . fig4 is a perspective view and fig5 is a left side view of the vicinity of the belts 7a , 7a . a two section - divided presser foot 8a , 8a is mounted swingably in the rear of a passing course c of the needle 3 to press the fabric from the lower surface . a pair of supports 4 , 4 are formed above the front end of the presser foot 8a , 8a . the fabric is held between the supports 4 , 4 and the presser foot 8a , 8a . above the rear end of the presser foot 8a , 8a , the feed dog 5 is provided confronting to the presser foots 8a , 8a . the feed dog 5 is driven by a feed bar 6 of the main body to perform an elliptical motion as shown in fig5 . in the lower half of the elliptical locus b , the feed dog 5 travels backward thereby to send the fabric 1 backward held between the presser foot 8a , 8a and the supports 4 , 4 . a pair of toothed belts 7a , 7a are arranged beneath the fabric passing area and in front of the passing course c of the needle 3 , interposing the presser foot 8a , 8a therebetween . the rear ends of the belts 7a , 7a are wound around belt pulleys 10 , 10 which are axially fitted in the holes at the front ends of the presser foot 8a , 8a and extend in a direction perpendicular to the fabric feeding direction . on the other hand , the front ends of the belts 7a , 7a are wound around one toothed belt pulley 12 having a rotary shaft 13 parallel to the shafts 11 , 11 of the belt pulleys 10 , 10 . both ends of the belt pulley 12 are supported by a u - shaped bracket 14 which is coupled to the presser foot 8a , 8a by a link mechanism , therefore , the bracket 14 moves up and down in association with the vertical motion of the presser foot 8a , 8a . an end of the shaft 13 of the belt pulley 12 projects from the bracket 14 , and a pulley 38 is provided at the projecting end . a toothed belt 37 is wound around both the pulley 38 and a pulley 35 provided in the final stage of a driving force transmission system which will be described later , thereby to transmit the driving force . consequently , the upper belts 7a , 7a travel backward . as is clear from fig3 on the main shaft 2 built in the arm 1b is mounted a known feed lift eccentric 20 to lift up the fabric closer to the pulley 9 which transmits the driving force from the motor ( not shown ). a ring formed at the upper end of a rod 61 is outfitted with the feed lift eccentric 20 on the side of the pulley 9 . a lid 19 is tightened by a screw 19a in order to prevent the rod 61 from slipping . on the left side in fig3 of the feed lift eccentric 20 is provided a feeding amount adjusting section 18 for intermittent driving and adjustment of the rotating amount of the belts 7a , 7a . the feeding amount adjusting section 18 is clearly illustrated in a disassembled perspective view , a lateral cross sectional view and a longitudinal cross sectional view of fig6 through 8 , respectively . the phase in fig7 is different from that of fig6 and 8 . an eccentric cylindrical bushing 72 is rotatably fitted around the main shaft 2 , and whose outer surface is eccentric to the main shaft 2 as indicated in fig6 . a plurality of holes 72a , 72a , . . . 20 are formed on the outer peripheral surface of the bushing 72 in positions with eccentricities proportional to the respective feeding amounts of the feed dog 5 of the main body thereby to determine the rotating amount of the belts 7a , 7a , i . e ., the feeding amount of the fabric toward the main body . moreover , a hole 72b is formed at an axially different position from the holes 72a in the peripheral direction of the bushing 72 . the positions of the holes 72a , 72a , . . . . sup .° are determined relatively to the structure of a feeding amount adjusting system of the feed dog 5 of the main body . on the left side of the eccentric bushing 72 in fig6 an eccentric pin mounting bed 73 is outfitted around the main shaft 2 and fixed thereto by screws 15 , 15 . the lower portion of the mounting bed 73 projects downward , where a pin hole 73a penetrates in a direction parallel to the main shaft 2 . a circular cylindrical pin 74a of an eccentric pin 74 is inserted into the pin hole 73a . a u - shaped fitting portion 74b open to the main shaft 2 at the end of the pin 74a is outfitted with a guide 69a of a feed adjusting unit 69 to be described later . the right side face of the mounting bed 73 touches the left side face of the eccentric bushing 72 . the feed adjusting unit 69 referred to hereinbefore is fixed to the eccentric bushing 72 rotatably on the right side of the mounting bed 73 . the feed adjusting unit 69 has an eccentric cylindrical portion 69c and a flange - like stopper 69d at the left end of the opening of the eccentric cylindrical portion 69c . the inner diameter of the eccentric cylindrical portion 69c is set slightly larger than the outer diameter of the eccentric bushing 72 . a rectangular guide 69a projecting leftward is formed at the lower end of the stopper 69d , which is slidably fitted into the fitting portion 74b of the eccentric pin 74 . the guide 69a has a hole 69b which opens upward at the upper end of the guide 69a . the fitting portion 74b of the eccentric pin 74 is guided by the guide 69a of the feed adjusting unit 69 to slide in a centripetal or centrifugal motion in accordance with the eccentricity of the adjusting unit 69 . a coil spring 70 and a ball 71 are inserted into the hole 69b of the guide 69a . a half of the ball 71 pushed by the coil spring 70 in a projecting direction from the hole 69b by the coil spring 70 into any of the holes 72a , 72a , . . . 20 of the eccentric bushing 72 , whereby the relative position between the outer peripheral surface of the eccentric bushing 72 and the feed adjusting unit 69 is fixed . by this fixing of the relative position , the eccentricity of the rotational axis of the feed adjusting unit 69 from the main shaft 2 is determined . in other words , the feeding amount varies owing to a combination of the eccentric cylindrical portion 69c and the eccentricity of the eccentric bushing 72 . at the upper end of a j - shaped rod 62 is formed a ring which is rotatably fitted around the cylindrical portion 69c of the feed adjusting unit 69 . a locking member 16 is penetrating the back of the arm 1b . when handling a button 16a of the locking member 16 outside the arm 1b , the tip of a button shaft 16b inside the arm 1b is inserted into the hole 72b of the eccentric bushing 72 , thus restricting the rotation of the eccentric bushing 72 , or the the tip of the button shaft 16b is pulled out from the hole 72b , thus allowing the rotation of the eccentric bushing 72 . as will be described later , the leading end of the j rod 62 swings in accordance with the eccentric rotation of the upper end thereof . as shown in fig3 and 9 , a small ring at the leading end of the rod 62 is rotatably coupled to one end of a handle 22 . the other end of the handle 22 is mounted to the right end of a transmission shaft 23 rotatably installed in a horizontal direction within the bed 1c . one end of a similar handle 25 is mounted to the left end of the transmission shaft 23 , and the leading end of a coupling arm 28 is rotatably coupled to the other end of the handle 25 . the leading end of the coupling arm 28 accordingly swings in response to the swing of the leading end of the rod 62 . fig9 is a disassembled perspective view of a driving force transmission mechanism from the rod 62 to the coupling arm 28 and further to the belts 7a , 7a in the succeeding stage . referring to fig2 a bearing block 29 fixed to the front face of the bed . 1c rotatably supports a shaft of a gear 30 in the horizontal direction . moreover , as indicated in fig9 to the left end face of the gear 30 the leading end of the coupling arm 28 is coupled swingably . the gear 30 meshes with a small gear 31 whose shaft is rotatably supported in the horizontal direction by the bearing block 29 , similarly . the small gear 31 is fixed around a rotary shaft 32 via a one - way clutch 31a . the bearing block 29 has also a one - way clutch 29a fitted therein so as to rotate the rotary shaft 32 in one direction as indicated by an arrow in fig9 . in the above - described structure , the rotary shaft 32 which is intermittently rotated in the arrow direction by the rotation of the gear 30 and the small gear 31 is intermittently driven to rotate in synchronization with the elliptical motion ( namely , intermittent movement ) of the feed dog 5 . the rotary shaft 32 is coupled to a shaft 34 via joints 33 and the shaft 34 is rotatably fitted into a bearing block 38 installed on the left side of the bearing block 29 . the pulley 35 of fig4 is mounted to a part of the shaft 34 being exposed from the bearing block 38 , and the toothed belt 37 is wound around the pulley 35 and the pulley 38 provided at the right end of the shaft 13 , thereby transmitting the intermittent driving force of the rotary shaft 32 to the belts 7a , 7a . meanwhile , a disc - like feed adjusting unit 63 is provided at the main shaft 2 near the boundary between the arm 1b and the head 1a in order to adjust the feeding amount of the feed dog 5 ( with reference to fig3 ). into a notch 63a formed on the periphery of the feed adjusting unit 63 , a locking member 64 projecting one end outside the arm 1b is able to be inserted . when the locking member 64 is inserted into the notch 63a , the main shaft 2 is restricted from rotating ( referring to fig2 ). since such technique as above is well known , the detailed description is omitted herein . the feeding operation of the fabric in the blindstitch machine of this invention will be depicted hereinafter . in the first place , the feeding amount of the feed dog 5 of the main body , that is , the seam length is adjusted corresponding to the thickness , kind , etc . of the fabric . the seam length is adjusted by rotating the pulley 9 after restricting the rotation thereof to insert the locking member 64 into the notch 63a of the feed adjusting unit 63 , and by matching a matchmark on the pulley 9 with a scale representing the desired seam length . the above operation is completely the same as in the conventional sewing machine of this kind . subsequently , in order to adjust the feeding amount of the feeding mechanism , the button 16a of the locking member 16 is handled to rotate the pulley 9 , then the button shaft 16b is inserted into the hole 72b of the eccentric bushing 72 , thus prohibiting the rotation of the eccentric bushing 72 . thereafter , the pulley 9 is rotated until the matchmark of the pulley 9 matches the scale of the same seam length . as a result , the ball 71 goes into the hole 72a of the eccentric bushing 72 corresponding to the feeding amount of the feed dog 5 , so that the relative position between the outer peripheral surface of the eccentric bushing 72 and the feed adjusting unit 69 is fixed . then , the locking member 16 is pulled out from the hole 72b . accordingly , as the pulley 9 is rotated by the motor ( not shown ), the needle 3 and the feed dog 5 act in the same manner as the conventional blindstitch machine . at this time , the eccentric pin mounting bed 73 is rotated in accordance with the rotation of the main shaft 2 , and therefore , the feed adjusting unit 69 is rotated via the eccentric pin 74 fixed to the mounting bed 73 . while the feed adjusting unit 69 rotates the eccentric bushing 72 with the ball 71 , since the outer peripheral surface of the eccentric bushing 72 is eccentric , the feed adjusting unit 69 fitted around the eccentric bushing 72 is rotated eccentrically to the main shaft 2 . in accordance with the eccentric rotation of the feed adjusting unit 69 , the upper end of the rod 62 fitted around the feed adjusting unit 69 rotate eccentrically as well , thereby swinging the leading end of the rod 62 . the swinging is transmitted to the coupling arm 28 via the handle 22 , transmission shaft 23 and handle 25 , to rotate the gear 30 . the rotation of the gear 30 is transmitted to the belt pulley 12 via the small gear 31 , the rotary shaft 32 rotating in one way and the toothed belt 37 , which invites the intermittent rotation of the belts 7a , 7a . the rotating amount of the belts 7a , 7a is determined by the position of the hole 72a of the eccentric bushing 72 into which the ball 71 is inserted , and which synchronize with the feed of the feed dog 5 . it is possible , however , to adjust the rotation of the belts 7a , 7a not to synchronize with the feed of the feed dog 5 depending on the sewing condition or the kind of the fabric . as this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof , the present embodiments are therefore illustrative and not restrictive , since the scope of the invention is defined by the appended claims rather than by the description preceding them , and all changes that fall within metes and bounds of the claims , or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims .