Abstract: The flow of a hydraulic fluid, which occurs under a sliding movement of a piston in a cylinder, is directly controlled by virtue of an extension-stroke pressure control valve and a compression-stroke pressure control valve. At the same time, the pressure in a back pressure chamber is varied, to thereby adjust the valve opening pressure for a main disk valve. This enables control of a damping force over a wide range. In each of the extension-stroke and compression-stroke pressure control valves, a thrust is generated in a slider due to a difference in pressure-receiving areas between a stepped portion of the slider and a sub disk valve in a valve chamber. The valve opening pressure is controlled, according to the balance between the thrust of the slider and a thrust of a proportional solenoid. By reducing the difference in the pressure-receiving areas in the valve chamber, the load applied to the proportional solenoid can be reduced.