PURPOSE: To simplify connection by providing a frame to a side edge of the rear side of a substrate, making an opening in the substrate section in the vicinity of the frame, and making use of a wall panel on the surface of the substrate to connect the frame to a base angle.

CONSTITUTION: A vertical piece 12 is extended upward from the outside end of an upper horizontal piece of a horizontal channel piece 11 in a base angle 1. After that, a plurality of slots 9 are made in the vertical piece 12. A wall panel 5 is formed of a substrate 2, a frame 3 and a tile 4. In addition, an opening 7 for executing clamping work is provided in the vicinity of a mounting hole 8 mounted to the substrate 2 and frame 3. Then, the base angle 1 is mounted with the horizontal channel piece 11 in a watertight state. Successively, the wall panel 5 is mounted on the upper horizontal piece of the horizontal channel piece 11 by using the vertical piece 12 as a guide. After that, a bolt is inserted into each of the slots 9 from the mounting hole 8 and is connected through the opening 7. According to the constitution, connection is firmly made, and a mounting working time can be reduced.