To effectively prevent a breakage of a plate when a gasket body formed of a rubber-like elastic material is integrally molded at both faces of the plate formed of a brittle material such as carbon. In order to attain this object, there is provided a method of manufacturing a plate-integrated gasket in which a gasket body formed of a rubber-like elastic material is integrally formed at both sides of a portion along a peripheral edge of a plate in the thickness direction, where an area located between gasket molding cavities defined by clamping the plate between split dies of a metal mold in the plate is formed to be a relatively thick portion at a position, facing an opening of a gate through which a molding material is injected into the cavities, and in the vicinity thereof.