An accumulator (100) includes: a housing (110) having an injection opening (112b) into which pressure gas is injected. A gas plug (150) seals the pressure gas in the housing (110). The housing (110) includes: a concave portion to which the gas plug (150) is fitted, and to which the gas plug (150) is welded with the welding portion (151) being melted on its bottom surface (110a). An inclined surface (110c) that extends from an edge portion of the concave portion toward an outside of the housing (110) such that a distance from a center of the injection opening (112b) increases, and the gas plug (150) includes a flange (152) which makes contact with the inclined surface (110c).