Secondary battery and method for manufacturing secondary battery

In a secondary batter, dead spaces between a wound electrode body and the inner peripheral surfaces of a rectangular battery case are made small. The secondary battery includes a wound electrode body in which a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet are superimposed and wound around a winding axis, and a rectangular battery case that houses the wound electrode body. The wound electrode body has a first flat surface, a second flat surface, a third flat surface, and a fourth flat surface positioned on the outer peripheral surfaces around the winding axis. The first flat surface and the second flat surface face each other with the winding axis interposed therebetween. The third flat surface and the fourth flat surface face each other with the winding axis interposed therebetween.