Thread cutting device for a sewing machine

A thread cutting device is adapted to be mounted under a bed of a sewing machine, and includes a mount having a marginal region which confronts a thread fetching zone, and a guide slot which is elongated parallel to a stroke path, a fixed knife disposed on the marginal region and having a blade aligned with the stroke path, a movable knife having a shank body which extends along the stroke path to terminate at actuated and hook ends, a drive unit disposed under the mount and having a rotatable output shaft to deliver a rotational force, and a rotation/translation conversion mechanism disposed to convert the rotational force into a translational force that is transmitted through the guide slot to actuate a translation of the actuated end of the shank body to thereby move the shank body between fetching and thread cutting positions.