A negative electrode includes a first region formed of a first material and a second region formed of a second material having a different ionization tendency from the first material. The negative electrode terminal includes a flange that is disposed so as to face the outer surface of a sealing plate. A sealing plate side insulating member is disposed between the flange and the sealing plate. A boundary between the first region and the second region has an exposed part that is exposed to the outside, and the exposed part is positioned at an opposite corner on the periphery of the flange to the sealing plate.