To prevent smoke and toxic gas from flowing from a space between an opening end of a wiring box and a wall material to the rear side of a wall.

A second seal material 22 is protruded so as to enclose an opening 11a of a fireproof and smoke insulation box 10. Then, the second seal material 22 is placed in close contact with an area around a through hole at a wall material Wa from the rear side of the wall material Wa. The structure seals a space between a front surface of the fireproof and smoke insulation box 10 and a rear surface of the wall material Wa. Thus, the structure prevents smoke and toxic gas from flowing to the rear side of the wall material Wa through the space between the wall material Wa and the fireproof and smoke insulation box 10.