the sewing machine is not operation the process waits until the holder 2 descends and also the sewing machine is in operation when detecting the operation of the sewing machine occurs then whether or not the fabric edge 17 covers the photosensor left 15a and photosensor right 15b is judged s6 and s8 in the case where the fabric edge 17 covers only the photosensor left 15a but not the photosensor right 15b that is the fabric edge 17 is properly fed by passing in the middle of the photosensor left 15a and the photosensor right 15b the step motor 10 is not operated so that the driven roller 5b is kept in its present position s10 and the process returns to step 4 in this case the engaging depth a of the driven roller 5b with the driving roller 5a is not changed in the case where the fabric edge 17 does not cover the photosensor left 15a that is the fabric edge 17 deviates leftward the step motor 10 is powered on so as to rotate counterclockwise in synchronism with this rotation the ball screw 7 rotates counterclockwise thereby ascending the driven roller 5b through the slider shafts 9 and the bracket 8 s7 as a result the engaging depth a of the driven roller.