A sealing device is provided which is capable of reducing its sliding resistance. In a sealing device 1 which is fitted into an annular groove formed in one of a housing with a shaft hole and a shaft inserted into said shaft hole and serves to seal an annular gap between these two members, and which includes a seal ring 2 made of a resin that is in sliding contact with the other of the two members, and an elastic ring 3 that is fitted between the seal ring 2 and the annular groove, the seal ring has a plurality of concave portions 22 formed on its sliding surface 20 which is in sliding contact with the other member.