To prevent forward/rearward movement of an axle during vehicle height adjustment by moving with an actuator a torque rod supporting the axle movably in the vertical direction, detecting an amount of the movement by detection means, and controlling the actuator based on detection results.

During vehicle height adjustment, a control unit 45 actuates an oil pump 39 to extend or compress a hydraulic suspension cylinder 1 and stretches a piston rod 37 by switching a solenoid valve 47 to a position A and feeding oil from an oil tank 41 to a double-acting hydraulic cylinder 35. The control unit 45 switches the solenoid valve 47 to positions A, B and N based on signals detected by stroke sensors 49, 53 disposed on the hydraulic suspension unit 1 and double-acting hydraulic cylinder 35, respectively. By moving a torque rod 17 in accordance with a stroke amount of the hydraulic suspension cylinder 1, forward or rearward movement of an axle can be prevented.