Abstract: A stator 3 of a motor 1 is pivotally supported on a stationary system 5 by an elastic member 28, 11a, 42 provided along the circumferential direction of the stator 3, and a detector 11 for detecting a rotational force of the stator 3 is provided to execute the control of stopping, accelerating, decelerating or reversing the operation of the motor 1 based on a detection signal from the detector 11. When the motor load is increased, transmission of torque from the action system 3 to the reaction system 4 of the motor 1 is cut off, and consequently the stator 3 itself of the motor 1 pivots with respect to the stationary system 5 as a reaction. In this stage, the detector 11 detects the rotational force of the stator 3 to stop, accelerate, decelerate, or reverse the operation of the motor 1.