A frame body comprises a first face portion on which a compressive force acts in case a load is applied, a second face portion on which a tensional force acts, and third and fourth face portions which connect the first and second face portions. The third and fourth face portions are respectively equipped with a reinforcing member which comprises a base portion which is away from the frame body and plural base portions which project from the base portion and are joined to the frame body. The convex portions have plural convexities which are arranged so as to extend both in the longitudinal and sectional directions of a frame.