To prevent the abnormal sound to occur when a vehicle suddenly starts off or accelerates by calculating the frequency variation between samplings one after the other, comparing the variation with a constant according to the acceleration evaluation condition, and attenuating the input signal with an adaptive filter having a smaller coefficient if the variation is found larger than the constant.

When a vehicle is in operation, a control section 31 samples the frequency based on signals sent from a revolution sensor 12 and calculates frequency variation Δf, and also evaluates whether large or small between the Δf and a constant α. As the Δf which is less than the α in normal travelling, becomes greater than the α when the stopper of an engine mount 20 touches an engine 11 due to sudden starting-off or acceleration, the frequency variation evaluation section converts the pulse signal before transmitting it to an adaptive filter, in which the amplitude and phase compensation are performed on the signal using a filter coefficient A×W which is smaller than an adaptive filter coefficient W used until then. This attenuates the output of a controlled system 48 and weakens the vibration force required to remove an external face.