PURPOSE: To obtain a damping force characteristic linearly changing in response to respective piston speeds by providing variable orifices in connecting passage from an open window formed against one of two disc valves arranged in series on one end face side of a piston to other chamber.

CONSTITUTION: During the expansion stroke with which a piston 2 reduces the volume of a liquid chamber A, operating liquid flows into a lower chamber B together with liquid pressure rise in the liquid chamber A. When the piston speed is low, a damping force characteristic proportional to the square of the speed due to constant sectional area of constant orifices 7i, 9g and variable orifices 15b, 15c, and a damping force characteristic proportional to the 2/3 power of the speed due to variable sectional area of a second expansion side disc valve 10, are obtained simultaneously. Thus, characteristic in which the rate of change is nearly constant can be obtained. When the piston speed is high, both expansion side disc valves 8, 10 are opened to obtain a damping force characteristic in which characteristics proportional to the 2/3 power of the speed are added in series. For the damping characteristic proportional to the 2/3 power of the speed, the rate of change in damping force is small, and nearly constant rate of change can be obtained. In the compression stroke, linear characteristic can also be obtained.