A gasket has a gasket main body which is made of a rubber-like elastic body, and a reinforcement body which is made of a material having a higher rigidity than the gasket main body. The gasket main body integrally has a tabular base portion, and a seal portion which is provided in an end portion in a width direction of the base portion, the reinforcement body is formed into a tabular shape, is set its thickness to be smaller than a thickness of the base portion, and is buried in the base portion in such a manner as to be exposed to a surface with one surface in a thickness direction of the base portion, and the reinforcement body is provided with a positioning hole for positioning the reinforcement body in relation to a metal mold forming the gasket main body on a plane.