A seal ring which maintains a stable sealing performance over a long term is provided. In a first seal portion 4, linear contact portions which come into linear contact with the sidewall surface of an annular groove on the unsealed fluid side are continuously extended over the whole circumference of the seal ring from one side of a separation portion 2 to the other side thereof, and the linear contact part provided at the convex part 21 of the separation portion 2, and the linear contact part provided at the concave part 24 of the separation portion 2 are located at a distance in the diametric direction of the seal ring.