PURPOSE: To improve the drivability and the comfortability, by controlling the damping force of the suspension automatically in accordance to the actual car speed thereby optimizing the damping force of the suspension in the preset car speed region.

CONSTITUTION: A car speed detecting means 1, meand 5, 6 for detecting whether the detected car speed is below the setting low car speed or above the setting high car speed and means 7 for holding the detected car speed signal for the predetermined interval and maintaining the suspension at the predetermined damping level, are provided. Consequently the damping force of the suspension is controlled automatically. For example when the low car speed detecting means 6 will produce the signal indicating that it is below 50km/h, the holding means 7 is disabled to stop the operation of the relay circuit 8 thus to deenergize the solenoid 9. Consequently the open valve of the suspension will open to increase the piston stroke and to reduce the damping force thereby the operation of the suspension is softened.