To facilitate the simple attaching of an external wall panel to compose a wing wall.

A wing wall is composed of various kinds of external wall panels 1, 20 to be attached so that the sides of their inner faces may be mutually opposite. In this case, a support metal fitting 40 is attached to a flat panel 1 and an outside angle corner which are previously attached with the outside angle corner partially left so as to front on the outside angle corner. The outside angle corner 20 to be finally attached is pushed in from the outside to engage frames 22, 22 on the side of their inner faces on the support metal fitting 40.