An object of the present invention is to easily detect a short circuit failure in a current collector of a prismatic battery and prevent a short circuit caused by an existence of a burr generated while cutting or a spatter generated while welding the current collector to an electrode plate. A battery unit is housed in a metallic battery case. In the battery unit, current collectors having bent portions on both sides are fixed to face surfaces of an electrode plate group of a prismatic battery. The portions of the battery case, which correspond to the bent portions, are pressed in a thickness direction. Under the pressure, a short circuit inspection for a short circuit between the battery case and the current collectors of the battery unit is executed. When a projected object exists on the bent portion, a short circuit is generated between the battery case and the current collector by pressing so that a short circuit failure caused by a shape of the current collector can be detected.