Abstract: A seal structure for pressure sealing between a fixed member and a movable member. The seal structure is made of a flexible seal member formed with two opposite edges, one edge being fixed to the fixed member, while the other edge lies against and contacts the movable member. A free part of the flexible seal member between the two edges thereof is generally bent around, as seen from the free part of the flexible seal member closest to its fixed edge looking towards its free part closest to its contact edge. A first space is defined on the generally concave side of the flexible seal member, and a second space is defined on the generally convex side of the flexible seal member. A higher fluid pressure present in the first space presses the contact edge of the flexible seal member firmly against the movable member.