SEALING DEVICE

A sealing device is disposed within a circumferential groove of an inner member that reciprocates relative to an outer member. An inner seal ring of the sealing device is made of a resin and includes an outer peripheral surface having a circumferential groove. An outer seal ring of the sealing device has a high elasticity and is fitted into the circumferential groove of the inner seal ring. The outer seal ring is brought into slidable contact with the inner peripheral surface of the hole of the outer member. A back ring of the sealing device has a high elasticity, is disposed radially inside the inner seal ring, and is compressed between the inner peripheral surface of the inner seal ring and the bottom wall surface of the circumferential groove of the inner member. Inclined surfaces are formed at both ends of the outer peripheral surface of the inner seal ring in the axial direction of the inner seal ring, each of the inclined surfaces having a diameter that decreases as a distance from a center of the outer peripheral surface of the inner seal ring in the axial direction increases. Protruding annular portions are formed at both ends of the inner peripheral surface of the inner seal ring in the axial direction, the protruding annular portions protruding radially inward to restrict movement of the back ring in the axial direction.