Seal ring

A seal ring having an annular shape and having one cut portion, the seal ring comprising:

• a pair of decreasing portions in which a radial-direction dimension of the seal ring decreases as the seal ring approaches the cut portion;
• and
• a plurality of recessed parts which are formed in at least one of surfaces directed in an axis line direction, wherein
• the plurality of recessed parts are configured with a first recessed part arranged in a range included in the decreasing portions and a second recessed part arranged in a range spaced apart from the cut portion with respect to the first recessed part,
• between an inner peripheral surface or an outer peripheral surface of the seal ring and the second recessed part, a wall part, which demarcates both of the inner peripheral surface or the outer peripheral surface and the second recessed part, and a communication portion, which causes both of the inner peripheral surface or the outer peripheral surface and the second recessed part to communicate with each other, are formed,
• between the inner peripheral surface or the outer peripheral surface of the seal ring and the first recessed part, an enlarged communication portion is formed which causes both of the inner peripheral surface or the outer peripheral surface and the first recessed part to communicate with each other,
• the enlarged communication portion is formed with one or a plurality of portions, and a total circumferential-direction dimension of the enlarged communication portion is greater than a circumferential-direction dimension of the communication portion.