A battery case for an electric vehicle includes a frame that has a polygonal frame shape in plan view, defines a through hole inside, and has R shapes provided on inner sides of corner parts of the polygonal frame shape. The case also includes a bathtub-shaped tray that includes a bottom wall located in the through hole, a surrounding wall that is provided around the bottom wall and defines an opening part on a side opposite to the bottom wall, and a flange that is provided at a distal end of the surrounding wall. The tray is pressure-welded to and integrated with the frame.