To improve sealing performance by constituting a reinforcing ring by an elasticity deformable first reinforcing ring to one member side by receiving a fluid pressire from the other member side and a second reinforcing ring having higher rigidity than the first reinforcing ring.

A reinforcing ring 4 comprises a first reinforcing ring 4A elastically deformable to a housing 2 side to be in a seal objective fluid side O of an axial direction part 4a and a second reinforcing ring 4B having higher rigidity than the first reinforcing ring not elastically deformed to be in an anti-seal objective fluid side A of the axial direction part 4a and a diametric direction part 4b. In a state of no pressure P in the seal objective fluid side O, the reinforcing ring 4A presses a seal part 6 with the reinforcing ring 4B to the housing 2. In a of the pressure P applied, the reinforcing ring 4A, deformed to a side of the housing 2 by receiving force due to the pressure P from a shaft 3 side, presses the seal part 6 to the housing 2 side. Contact surface pressure distribution relating to the housing 2 is changed by mounting and compression of the seal part 6 by the pressure P, the highest value of contact surface pressure rises, and seal performance of the seal part 6 is improved.