PURPOSE: To control a suspension system in consideration of various conditions of a road surface and a vehicle.

CONSTITUTION: A force actuator 11 is connected between a vehicle body and each wheel. A position sensor 66 senses displacement between the vehicle body and each wheel and provides a position signal 67. An acceleration sensor 60 senses the vertical inertial acceleration of the vehicle body relative to the ground at each wheel and provides an acceleration signal 61 indicative of the vertical inertial acceleration. A controller 70 including a digital signal processor 80 determines a velocity signal based on each acceleration signal and a plurality of modal forces including heave, pitch and roll modal forces which act on the vehicle body. A force actuator control signal 94 at each wheel is produced based on a plurality of modal forces, and a drive circuit 95 applies a force actuator control signal 96 to the associated force actuator 11.