The flow of hydraulic fluid induced by sliding movement of a piston in a cylinder is controlled by a pilot-type main valve and a pilot valve to generate damping force. The valve opening of the main valve is controlled by adjusting the pressure in a pilot chamber through the pilot valve. A volume compensating chamber is defined by a flexible disk member so as to face the pilot chamber. The volume compensating chamber is communicated with a reservoir through communicating passages. When the disk valve opens, the volumetric capacity of the pilot chamber reduces. At this time, the flexible disk member deflects toward the volume compensating chamber, thereby suppressing an excessive rise in pressure in the pilot chamber and preventing an unstable operation of the pilot valve and the main valve to obtain a stable damping force.