PURPOSE: To always generate optimum damping force by actuating an air cylinder by the internal pressure of an air spring suspending an axle to a car body and also varying the damping force of the shock absorber installed between the axle and the car body by the internal pressure of the air cylinder.

CONSTITUTION: A wheel 10 is suspended from a frame 9 by a suspension comprising a leaf spring 11 and an air spring 12. A shock absorber 16 is installed between the leaf spring 11 and a frame bracket 17. In such device, the shock absorber 16 is provided with a lever 27 for adjusting damping force, which is connected to the piston rod 29 of an air cylinder 28. When the internal pressure of the air spring 12 is increased, for example, this internal pressure is supplied to the air cylinder 28. This pressure supplying allows the piston rod 29 to move opposing to a return spring 30 for rotating the adjusting lever 27 resulting in the improvement in the damping force of the shock absorber 16.