A first projecting portion is disposed between a head portion of an external terminal and a gasket body of a gasket, the first projecting portion projecting toward the gasket body from a first opposedly-facing surface which opposedly faces a case of the head portion, the first projecting portion surrounding the shaft portion, the first projecting portion having a pressing surface which directly or indirectly presses the gasket body in a projecting direction of the first projecting portion. The gasket has the second and third opposedly-facing surfaces, the second opposedly-facing surface opposedly facing the head portion, the third opposedly-facing surface opposedly facing the case. A second projecting portion is disposed in a region of at least one of the second and third opposedly-facing surfaces which correspond to the first projecting portion, the second projecting portion surrounding the shaft portion and being in a state where the second projecting portion is compressed toward the second or third opposedly-facing surface by the pressing surface.