PURPOSE: To perform a stable operation without torque interference between loads by detecting the speed variation of a torque control system by an incomplete differentiator, and applying the calculated result to the output of a torque control loop as a correction signal.

CONSTITUTION: A speed signal of N2 output from a speed calculator 23 for a second motor is input to a variation suppression circuit 30 composed of an incomplete differentiation calculator, and the variation component of the speed signal N2 is separated. As a result, a torque variation T output from the variation suppression circuit is added in reverse polarity to a motor generating torque output from a torque regulator 22. As a consequence, since the speed N2 of the second motor 20 is made constantly, variation in a rotating angle position θ2 can be suppressed. Thus, fluctuation of torque caused by the resonance of a machine system can be suppressed.