PURPOSE: To reduce all vibration in a multidegree of freedom system by a method wherein a feedback signal forms a vibration response (a speed component), classified by a single frequency, to each natural frequency of an object to be dampered.

CONSTITUTION: A signal processing part factorizes an input signal into a vibration response (a speed component), classified by a single frequency, to each natural frequency of an object to be dampered by using a narrow band-pass filter 5. After multiplication of each signal by a feedback gain by means of a voltage amplifier 6, a phase is inverted by a phase inverter 7, where occasion demand, so that feedback control is stabilized. Composition of results is effected by an adder 8 to provide a control signal having frequency characteristics as shown in a diagram. A control signal converted in a manner described above by the signal processing part is inputted to a power amplifier 9 to drive an actuator 2. In this way, a feedback control system using an output (the speed component of a response separated classified by a signal frequency) is formed, and the generation of all vibration of an object to be damped is reduced.