During either of the extension and compression strokes, hydraulic liquid flows from a cylinder upper chamber into a reservoir through an annular passage and a damping force control mechanism, and a damping force is generated by the damping force control mechanism. The check valve is provided with a sub-check valve in parallel thereto, which opens in a very low piston speed region to allow the hydraulic liquid to flow through an orifice passage. These check valves are opened successively as the piston speed increases, thereby generating a sufficiently small damping force in the very low piston speed region during the compression stroke of the piston rod, and obtaining a moderate damping force when the piston speed increases.