A seal ring (100) makes contact with a low-pressure-side (L) side wall surface of an annular groove (510) and slides against an inner circumferential surface of a shaft hole of a housing (600) through which a shaft (500) is inserted. The seal ring includes a pair of concave portions (130) extending in a circumferential direction on an outer surface, wherein a distance between a side surface on one side of a convex portion (120) that is disposed between the pair of concave portions (130) and a side surface on another side of the seal ring (100), and a distance between a side surface on another side of the convex portion (120) and a side surface on one side of the seal ring (100) are set to be shorter than a distance between an inner circumferential surface of the seal ring and an outer circumferential surface of the convex portion (120).