A seal ring that seals an annular gap formed between a shaft and a housing that has a shaft hole into which the shaft is inserted. The seal ring is configured such that one of both the ends and has a projection projecting in the direction of the circumference of the seal ring. The other end has a recess used in combination with the projection. The seal ring is characterized in that the recess has an inclining side face, which inclines from the direction of the circumference, and the projection and the recess form a sliding part so that a part of the edge of the leading end of the projection slides over the inclining side face of the recess, and portion of the sliding part is formed as a linear sliding portion.