A gasket is to be disposed in a compressed state between a groove bottom surface defining a gasket groove formed in a first member and a seat surface of a second member so as to make a hermetical sealing between the groove bottom surface and the seal surface. The gasket includes a first seal section formed at an end part of the gasket in a compression direction. The first seal section is ridge-shaped so as to become slender in a direction toward a tip portion of the first seal section. The first seal section has first and second side surfaces which are opposite to each other with respect to a first plane passing through the tip portion of the first seal section. The first side surface overhangs outwardly larger than the second side surface.