A sliding seal seals an annular gap between a first member and a second member to separate a high-pressure side and a low-pressure side from each other, the first member being movable relative to the second member. The sliding seal is provided at an annular attaching groove provided at the second member. The sliding seal includes: a pressure fluid seal configured to slidingly contact a sliding surface of the first member; and a lubricant holding piece provided at the high-pressure side of the pressure fluid seal, a lubricant storage space being formed between the lubricant holding piece and the pressure fluid seal.