Abstract: A rotating disc driven in synchronism with the reciprocating movement of the needle of a sewing machine has a plurality of cutaway arc-shaped sections having different arcs to produce a pulse train of frequency related to the motor speed. A photoelectrical device responds to intermittent light the interceptions being caused by the rotating disc. The pulse train comprises pulses of different pulse lengths, each corresponding to the lower and upper dead points of the needle. First and second pulse length detectors are provided to detect sequentially each of the pulse lengths in a controlled manner by the operator manipulation of a treadle so that the motor is decelerated from a preselected speed to a standstill with the needle at its lower or upper dead point.