A highly safety cell is provided in which short-circuiting is unlikely to occur. In order to prevent short-circuiting, for example, burrs generated when a laminate film used as an exterior packaging material is cut are prevented from penetrating an interior resin layer of the laminate film. When an electrode terminal extension side of the laminate film is thermal welded, heating and compression are performed by a heater head on a part of the laminate film apart from the edge portion thereof so that the thickness of the above edge portion is larger than that of a thermal welded portion. In addition, thermal welding is performed so that the thickness of a thermal welded portion including an electrode terminal is larger than that of a thermal welded portion including no electrode terminal, and as a result, short-circuiting can be more effectively prevented.