To reduce cost by providing a concrete slab, an aluminum plate attached to the surface of the concrete slab, and a fixing fittings and cushion members attached to rear surface of the aluminum plate.

Fixing fittings 3 are attached to predetermined places on the rear surface of an aluminum plate 2, and cushion members 4 consisting of sponge or rubber are wound around the fixing fittings 3. Next, the aluminum plate 2 is set in a formwork with the rear surface facing upward, concrete is poured in the formwork, and a concrete slab 1 provided with a recessed portion 7 for housing the fixing fittings 3 is formed. Then, the fixing fittings 3 are intruded into the recessed portion 7 of the concrete slab 1, and the aluminum plate 2 and concrete slab 1 are combined together to one united body, and sealing 6 is applied to a recessed portion 5 provided in the concrete slab 1. Thus, no assembly of backing is required so that no work is needed for installing and disassembling scaffolds or the like, thereby reducing the cost.