PURPOSE: To control left and right cam stitches simply by the extent of rotation of a specific annular grooved cam rotated with a motor by operating the left and right cam stitches through a pair of rocking pieces, fitted and engaging with the aforementioned annular grooved cam provided in a rotating disk.

CONSTITUTION: A tumbler-shaped annular grooved cam 8 of a small circular arc groove (8a) continuous to eccentric grooves (8b) and (8b) is formed in a rotating disk rotating by a prescribed extent on a signal to a driving motor. Both ends of the groove (8a) are taken as basic positions (a) and (a'). One end each is fitted and engaged with the basic positions (a) and (a') so that a pair of rocking pieces 10 and 11 having the base ends (10b) and (11b) supported on shafts at symmetrical positions may be an interlocking mechanism with left and right cam stitches 2 and 2. The extent of stitch can be regulated with the grooves (8b) while keeping the other cam stitch in an inoperative state with the groove (8a).