Abstract: A gasket for sealing a space between a first member and a second member fastened by a fastening member so as to face each other, the gasket being fitted in an annular mounting groove formed on one of facing surfaces of the first member and the second member. The gasket is provided with an annular gasket body formed along the mounting groove; a plurality of longitudinal ribs, made up of protruding bodies, provided on a side surface of the gasket body facing a side wall of the mounting groove, the longitudinal rib protruding along height direction corresponding to depth direction of the mounting groove of the gasket body and protruding at intervals in circumferential direction of the gasket body; and a transverse rib provided on the side surface, the transverse rib being made up of a protruding body continuously protruding over the entire circumference of the gasket body.