To prevent a connection part from coming-off or meandering due to thermal expansion of molding materials by passing screws through screw holes provided on a molding joint and slotted holes provided on the end parts of horizontal molding materials, and fastening the screws to fixtures.

Fixtures 4, 4 are respectively fitted to wall bodies 2, 2 on both sides of an external angle part of a building unit 1, and the mutual end parts of horizontal molding materials 3, 3 are placed on the respective fixtures 4. Next, the end parts of both horizontal molding materials 3 are covered with a L-shaped molding joint 5. Screws 6 are passed through the screw holes 51, 51 provided on the molding joint 5, and slotted holes 31 provided in the lengthwise direction of the molding materials 3, and fastened to the fixtures 4. Hereby, the molding material 3 can be moved by the length of the slotted hole 31, expansion of the molding materials 3 are absorbed by the connection part, the connection part can be prevented from being injured so as to come-off, and the molding material 3 can be prevented from bending.