A cloth cutting knife driving device is capable of being released, through an interlocking connection between an upper knife rocking arm and a sewing machine main shaft. The device includes a drive shaft, which is able to swing rotatably, by interlocking with a main shaft, a rocking arm rotatably supported on the drive shaft at one end providing a rocking motion, and a cloth cutting knife supported at the one end of the rocking arm that is rigidly held in a cloth cutting position or an inactive position, which is vertically displaced through the motion of the arm. The device has a coupled and released state between the drive shaft and rocking arm, which are brought about by an engaging part on the drive shaft and a movable member, movable relative to the rocking arm in a direction perpendicular to an axis of the drive shaft.