To eliminate the need of an operation for performing work matched with the shape of the projected part of a beam by attaching a plate material for closing a part between a cabinet back surface and a wall surface at the lower part of the projected part of the beam to the lower surface or back surface lower end of a cabinet attached to the wall surface where the beam is projected.

On the wall surface 2 where a concrete beam 1 is projected, a side plate, a top plate, a bottom plate and a back plate are assembled by the wood material of thickness 15 mm and this cabinet 3 with a door is attached by a screw 3b for concrete. Then, on the lower surface of the cabinet 3, a plate material 4 made of stainless provided with a manually bendable attaching part 5 is attached through a through-hole by the screw 6. In the meantime, the manually bendable attaching part 7 is also provided on the opposite side of the plate material 4 made of the stainless and the plate material 4 is attached to the wall surface 2 through the through-hole by the screw 8 at the attaching part 7. Thus, the part between the back surface of the cabinet 3 and the wall surface 2 is easily closed.