A piston connected to a piston rod is fitted into a cylinder in which a hydraulic fluid is sealably contained. A flow of the hydraulic fluid is generated in an extension-side fluid passage and a compression-side fluid passage according to a sliding motion of the piston, and this flow of the hydraulic fluid is controlled by a main disk valve, to thereby generate a damping force. A valve-opening pressure of the main disk valve is controlled by an internal pressure of a back-pressure chamber generated due to a difference in flow path area between a back-pressure chamber inlet fluid passage and a downstream-side orifice. During a reverse stroke, a check valve is opened, to thereby introduce a pressure in a downstream-side cylinder chamber into the back-pressure chamber, so that the main disk valve can be maintained in a closed position and a stable damping force can be generated.