PURPOSE: To release the constraint of a needle thread at a desired time point in the course of stop of sewing by driving an electromagnetic actuator in accordance with a command signal, and constituting the sewing machine so that the sewing machine main shaft is rotated until an engaging link is driven to oscillate by an operating part of a cam.

CONSTITUTION: When a thread cutter button is operated, a thread cutter signal is outputted from a thread cutter switch, and a sewing machine motor is driven to rotate at a low speed, and simultaneously, an electromagnetic actuator 100 and 130 which is not shown in the figure are energized, therefore, a movement of a movable blade is started, and also, an operating pin 96 and an engaging link 97 are moved to a release position through a turning member 102, and an engaging arm 97b is engaged to a first cam 93. As a result, since a tension release lever turns to an operating position by the operating pin 96, a thread tension disc is separated from a thread tension disc and tension of a needle thread is released. On the other hand, when a phase angle of a main shaft 13 is about 300°, oscillation of the engaging link 97 is started and a movable wheel 71 is separated from a thread guide control plate 70, therefore, constraint of the needle thread by a thread passing controller 72 is released after 300° phase angle.