PURPOSE: To prevent deterioration of suspension controllability caused due to drift of excessive low frequency signal input by furnishing a speed changing means to change a spring upper and lower acceleration signal to a spring upper and lower speed signal in accordance with a phase lag compensatory expression.

CONSTITUTION: A signal from each of upper and lower acceleration sensors 1 is changed to a spring upper and lower speed signal at each of tower positions by using a phase lag compensatory expression at a block B1. This signal is sent to a block B2 which is a band pass filter, and components except for a target frequency band to carry out control are blocked. Relative speed between spring and unspring at each of tower positions is found by using a transfer function from each of the upper and lower acceleration sensors 1 at a block B3. at the time of finding the spring upper and lower speed signal from a spring upper and lower acceleration signal, as it is found in accordance with the phase lag compensatory expression, it is possible to prevent deterioration of suspension controllability caused by drift due to excessive low frequency signal input.