An electrode group 4 having a positive electrode plate and a negative electrode plate arranged with a porous insulating layer interposed therebetween and end portions of the positive and negative electrode plates protruding from the porous insulating layer is prepared, and current collector plates 10 and 11 each of which is provided with a projection 12 having a gap 12a formed therein is prepared. With the end portion 2a of the electrode plate protruding from the porous insulating layer 3 kept in contact with a principle surface of the current collector plates 10 and 11, the projection 12 is locally heated to join the end portion 2a of the electrode plate and the current collector plates 10 and 11. the end portion 2a of the electrode plate is welded to the current collector plates 10 and 11 with a fused material obtained by fusing the projection 12.