To automatically set a differential gain again only by setting characteristics of a machine system again.

A Fourier inverse transformer 3 generates an operation value b* (AC signal) on the basis of an amplitude A* and a frequency F*. This operation value b* is supplied to an inverter 11 to control the torque of a motor 12. Further, a differential gain computing element 82 calculates the differential gain D' of a differentiator 80' on the basis of a constant C. The differentiator 80' differentiates a controlled variable aT fed back from the motor 12 according to the said differential gain d' and supplies the result to a deviation detection point 81. Therefore, the operation value supplied to the inverter 11 is (b*-D's.TK/ KT). Then the resonance gain of the whole system can be adjusted with the fed-back differential gain of the differentiated value of the detected torque to suppress the resonance of the machine system, and even when a controlled system is changed, the differential gain D' of the differentiator 80' is set again automatically.