Abstract: Herein disclosed is a control unit for providing seam length control of a sewing machine which comprises: a main shaft; a sewing needle in accordance with the rotations of the main shaft for forming stitches in a work fabric which is placed on a work supporting surface so that it may be sewn; a feed dog for feeding the work fabric while passing a sewing point of the sewing needle; a work feed mechanism including a feed bar for carrying the feed dog and a feed shaft for supporting the feed carriage, the work feed mechanism being adapted to impart motions in a feeding direction to the feed dog by the reciprocating rotations of the feed shaft in accordance with the rotations of the main shaft; and mechanical adjusting means interposed between the work feed mechanism and the main shaft for adjusting a feed pitch of the feed dog by changing the reciprocating stroke of the feed shaft.