PURPOSE: To secure an excellent leakage preventive effect by installing two tubular valve elements parallelly in an impulsive part, and constituting them to open or close their passages according to the impulsive direction each, in a one-way valve system which is interposed between a cylinder and a piston, and allows a one-way flow of fluid between two spaces themselves.

CONSTITUTION: A one-way valve system being installed in space between a cylinder 2 of a compressor and a piston 3, being fitted in this cylinder, is provided with two piston rings 4, 5 to be fitted in a peripheral groove 3a formed on a peripheral wall of the piston 3 and a tension ring 6 for energizing these piston rings 4, 5 to be pressed to an inner wall of the cylinder 2, respectively. At the time of a compressive process of the piston 2, a side face at the side of a counter discharge chamber of the piston ring 5 is pressed to an opposed surface of the peripheral groove 3a, thereby preventing any fluid leakage from occurring so surely. Inversely, at the time of an expansion process, the side face of the discharge chamber side of the piston ring 4 is pressed to the opposed surface of the peripheral groove 3a, whereby the opposed surface themselves of the piston ring 5 and the peripheral grooves 3a are separated from each other, producing a clearance there, thus a movement to the side of a fluid discharge chamber 7 is allowed.