PURPOSE: To prevent the generation of impact noise at the operation stop time in an active suspension device by inputting an electric signal corresponding to the cylinder pressure before releasing electric signals to a solenoid proportional relief valve so as to maintain a control valve in the setting work state.

CONSTITUTION: With an ignition switch turned off, the cylinder pressure of a hydraulic cylinder 2 is detected by a sensor 1 and inputted into a controller. The controller outputs a signal proportional to this cylinder pressure to a control valve 4 so as to control the cylinder pressure of the hydraulic cylinder 2 to be the pressure at the resting time of a hydraulic system, that is, to maintain the expansion state of the hydraulic cylinder 2. The controller then releases specified signals to a solenoid proportional relief valve 8a gradually. With this constitution, the generation of valve impact noise can be prevented.