A seal ring for sealing an annular clearance between two members installed rotatably relative to each other, wherein a relief part (5) is provided in the two members on the side surface sides corresponding to the slide wall surface (72) of an annular groove (71) all around the periphery thereof so that the radial width thereof becomes smaller near a separated part (2) and larger at positions apart from the separated part (2) and gradually varies at a portion for transition from the smaller width portion to the larger width portion.
