A sealing structure which is provided with: a shaft and a housing being rotatable relative to each other; and a sealing device which is fitted into an annular groove formed in an outer periphery of the shaft so as to seal an annular gap between said shaft and the housing while they rotate relative to each other, thereby to hold a fluid pressure in a region to be sealed which is constructed such that the fluid pressure therein changes, the sealing device comprising: an outer peripheral ring made of resin that is in intimate contact with a side wall surface of said annular groove at a low pressure side thereof, and slides with respect to an inner peripheral surface of a shaft hole in said housing through which said shaft is inserted; and an inner peripheral ring made of a rubber-like elastic body that is in intimate contact with an inner peripheral surface of said outer peripheral ring and a groove bottom surface of said annular groove, respectively, thereby to push said outer peripheral ring toward an outer peripheral surface side thereof; characterised in that said outer peripheral ring is formed on its outer peripheral surface with a concave portion which extends from an end of a high pressure side to a position which does not arrive at an end of a low pressure side, so as to introduce fluid thereinto from the high pressure side. a shaft and a housing being rotatable relative to each other; and a sealing device which is fitted into an annular groove formed in an outer periphery of the shaft so as to seal an annular gap between said shaft and the housing while they rotate relative to each other, thereby to hold a fluid pressure in a region to be sealed which is constructed such that the fluid pressure therein changes, the sealing device comprising: an outer peripheral ring made of resin that is in intimate contact with a side wall surface of said annular groove at a low pressure side thereof, and slides with respect to an inner peripheral surface of a shaft hole in said housing through which said shaft is inserted; and an inner peripheral ring made of a rubber-like elastic body that is in intimate contact with an inner peripheral surface of said outer peripheral ring and a groove bottom surface of said annular groove, respectively, thereby to push said outer peripheral ring toward an outer peripheral surface side thereof; characterised in that said outer peripheral ring is formed on its outer peripheral surface with a concave portion which extends from an end of a high pressure side to a position which does not arrive at an end of a low pressure side, so as to introduce fluid thereinto from the high pressure side. an outer peripheral ring made of resin that is in intimate contact with a side wall surface of said annular groove at a low pressure side thereof, and slides with respect to an inner peripheral surface of a shaft hole in said housing through which said shaft is inserted; and an inner peripheral ring made of a rubber-like elastic body that is in intimate contact with an inner peripheral surface of said outer peripheral ring and a groove bottom surface of said annular groove, respectively, thereby to push said outer peripheral ring toward an outer peripheral surface side thereof; characterised in that said outer peripheral ring is formed on its outer peripheral surface with a concave portion which extends from an end of a high pressure side to a position which does not arrive at an end of a low pressure side, so as to introduce fluid thereinto from the high pressure side.