An electrode group (4) where a positive electrode plate (1) and a negative electrode plate (2) are arranged through a porous insulating layer (3) in such a manner that the end portions of the positive electrode plate (1) and the negative electrode plate (2) protrude from the porous insulating layer (3), and current collecting plates (10, 11) each provided with a protrusion (12) having a gap (12a) on the inside are prepared. While bringing the electrode plate end portion (2a) projecting from the porous insulating layer (3) into contact with a major surface of the current collecting plates (10, 11), the protrusion (12) is heated locally to bond the electrode plate end portion (2a) and the current collecting plates (10, 11), and the electrode plate end portion (2a) is welded to the current collecting plates (10, 11) by a molten member obtained by melting the protrusion (12).