A flat-shaped winding electrode body in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween includes a positive electrode tab portion and a negative electrode tab portion at one end in a direction in which a winding axis of the winding electrode body extends. Two pieces of the flat-shaped winding electrode body are housed in a prismatic outer body so that the winding axis of each piece is disposed in a direction perpendicular to a sealing plate, and the positive electrode tab portion and the negative electrode tab portion are located on one end of the winding electrode body closer to the sealing plate than the other end.