folding a strip of positive electrode plate formed of a plurality of positive electrode layer faces coupled together by a plurality of connecting pieces, and a strip of negative electrode plate formed of a plurality of negative electrode layer faces coupled together by a plurality of connecting pieces at the respective connecting pieces and coiling it around into an electrode plate group of flat form such that the positive electrode layer faces and the negative electrode layer faces are alternately layered upon one another with a separator interposed therebetween;

accommodating the electrode plate group into a sealing case;

injecting liquid electrolyte thereinto;

placing a cap case onto the sealing case via a gasket; and

crimping the cap case to seal the inside of the sealing case, characterized in that

the positive electrode plate and the negative electrode plate are respectively formed with positional discrepancy detecting cut-outs for detecting positional displacement between the positive electrode layer faces and the negative electrode layer faces when both electrode plates are coiled around;

after coiling around the positive electrode plate and the negative electrode plate into the electrode plate group, X-rays are irradiated thereto in a direction in which the electrode plates are layered so as to obtain transmitted X-ray images of the electrode plate group;

a positional discrepancy is detected, by processing the images, between the positional discrepancy detecting cut-outs in the positive electrode layer faces and the positional discrepancy detecting cut-outs in the negative electrode layer faces; and

when the detected positional discrepancy is within a predetermined permissible range, the electrode plate group is accommodated in the sealing case.