A shaft core includes a positive electrode shaft core portion having a positive electrode splaying portion at one end, a negative electrode shaft core portion having a negative electrode splaying portion at the other end, and an insulation portion that mutually insulates and integrates the positive and negative electrode shaft core portions. The positive electrode plate is electrically connected to the positive electrode collector in a state of being splayed through the positive electrode splaying portion, and the negative electrode plate is electrically connected to the negative electrode collector being splayed through the negative electrode splaying portion. The positive and negative electrode shaft core splaying portions press and open their respective electrode laminates at the end surfaces of the wound electrode group, the positive electrode connection piece and the positive electrode collecting portion are welded, and the negative electrode connection piece and the negative electrode collecting portion are also welded.