Even creep due to thermal expansion is reduced in the circumferential length occurs hemline, and aims to provide a sealing device which can maintain the sealing property during the fluid pressure load with a simple structure, its object is a housing having a shaft hole, to the annular gap between the shaft performing housing relative sliding movement while being inserted into the shaft hole to seal the fluid, is mounted in an annular groove formed on the outer peripheral surface of the shaft a resin-made annular body, a sealing device having a cut portion on the circumference of the annular body, and the seal ring portion having an outer peripheral surface side sliding surface which slides with the housing, the inner circumference of the seal ring portion provided on the surface side, the tip is a lip portion disposed in the groove bottom of the annular groove, lip, by a fluid pressure when the fluid pressure load, the tip is in contact with the groove bottom of the annular groove expanding the distance between the groove bottom of the sealing ring portion and the annular groove Te It is provided to be deformed in the direction to be solved by the sealing device according to claim.