A hollow structure includes: a main portion having an inner circumferential surface; and a flange portion including a first overhanging portion and a second overhanging portion that protrude outward from an outer circumference of the main portion and face each other. A first surface of the first overhanging portion and a second surface of the second overhanging portion are continuous with the inner circumferential surface, and the flange portion has a joint portion at which the first surface and the second surface are joined together. The main portion and the flange portion are formed of a metal material composed mainly of a light metal, and the formula ⅕