Abstract: A low speed adaptor for use in a sewing machine driven by a main motor, particularly to one which employs a main transmission belt and an auxiliary transmission belt to change the speed of the sewing machine from high to low. This main transmission belt passes over the belt pulley of the main motor, then over the transmission belt pulley of the adaptor, and then over the belt pulley of the sewing machine; while, the auxiliary transmission belt passes over the belt pulley of the auxiliary motor and over the belt pulley of the adaptor body. The adaptor comprises an electromagnetic clutch and brake device capable of selectively switching the drive of the sewing machine from the main motor operating at high speed to the auxiliary motor operating at low speed.