A molding device is provided with a holding portion for clamping the end of an extruded portion, and a cavity for forming a molded portion. The holding portion has holding cores to come in contact with the end of the extruded portion, and at least a part of the holding cores is formed by a material with a low thermal conductivity. Thus, the molding method of a weather strip includes, clamping the end of the extruded portion by the holding portions, then, ejecting or injecting a rubber material for molding the molded portion in the cavity, and then, molding the rubber by vulcanization.