A method of manufacturing a gasket, the gasket comprising: a gasket main body which is made of a rubber-like elastic body; a reinforcement body which is made of a material having a higher rigidity than the gasket main body; the gasket main body integrally having 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 being formed into a tabular shape, being set its thickness to be smaller than a thickness of the base portion, and being buried in the base portion; and the reinforcement body including a positioning hole, the method comprising the steps of: preparing a metal mold having a cavity which forms the gasket main body, and a molding material injection port which injects a molding material into the cavity; making the molding material injection port open to a position which laps on a plane over the reinforcement body which is set to a fixed position within the cavity; and injecting the molding material from the molding material injection port to the cavity while pressing the reinforcement body to an inner surface of the cavity, characterized in that the metal mold has a positioning convex portion provided on a plane surface of the base portion forming portion in an inner surface of the cavity, for positioning the reinforcement body in relation to the metal mold on a plane surface, the reinforcement body is set to a fixed position within the cavity by fitting the positioning hole to the positioning convex portion, and the reinforcement body is pressed to the inner surface of the cavity with an injection pressure for injecting the molding material when the molding material is injected from the molding material injection port to the cavity, the reinforcement body being buried in the base portion in such a manner as to be exposed to a surface of the base portion with one surface in a thickness direction of the base portion. a gasket main body which is made of a rubber-like elastic body; a reinforcement body which is made of a material having a higher rigidity than the gasket main body; the gasket main body integrally having 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 being formed into a tabular shape, being set its thickness to be smaller than a thickness of the base portion, and being buried in the base portion; and the reinforcement body including a positioning hole, the method comprising the steps of: preparing a metal mold having a cavity which forms the gasket main body, and a molding material injection port which injects a molding material into the cavity; making the molding material injection port open to a position which laps on a plane over the reinforcement body which is set to a fixed position within the cavity; and injecting the molding material from the molding material injection port to the cavity while pressing the reinforcement body to an inner surface of the cavity, preparing a metal mold having a cavity which forms the gasket main body, and a molding material injection port which injects a molding material into the cavity; making the molding material injection port open to a position which laps on a plane over the reinforcement body which is set to a fixed position within the cavity; and injecting the molding material from the molding material injection port to the cavity while pressing the reinforcement body to an inner surface of the cavity, characterized in that the metal mold has a positioning convex portion provided on a plane surface of the base portion forming portion in an inner surface of the cavity, for positioning the reinforcement body in relation to the metal mold on a plane surface, the reinforcement body is set to a fixed position within the cavity by fitting the positioning hole to the positioning convex portion, and the reinforcement body is pressed to the inner surface of the cavity with an injection pressure for injecting the molding material when the molding material is injected from the molding material injection port to the cavity, the reinforcement body being buried in the base portion in such a manner as to be exposed to a surface of the base portion with one surface in a thickness direction of the base portion.