The thickness of a terminal connection portion of a positive electrode current collector is greater than that of a terminal connection portion of a negative electrode current collector. The terminal connection portion of the positive electrode current collector has a through-hole, and a positive electrode terminal is inserted into the through-hole and is upset on the terminal connection portion. The terminal connection portion of the negative electrode current collector has a through-hole, and a negative electrode terminal is inserted into the through-hole and is upset on the terminal connection portion. A recessed portion is formed in a lower surface of the positive electrode terminal connection portion around the through-hole, and a lower end portion of the positive electrode terminal is disposed in the recessed portion.