To improve the openness of an opening section while enhancing the design properties of a room when fittings are to be installed at the opening section of the wall of the room.

One strip of an upper groove section 92 is formed along the longitudinal direction to the underside 91 of a ceiling cornice 9 being abutted and mounted to a wall panel 5 and a ceiling 2 and ending the wall panel 5 and the ceiling 2 extending over approximately overall width while one strip of a lower groove section 12 is formed along the longitudinal direction to the top face 11 of a plinth 10 being abutted and fitted to the wall panel 5 and a floor panel 3 and ending the wall panel 5 and the floor panel 3 extending over approximately overall width. Sliding doors 7, 7 being freely moved along the upper groove section 92 and the lower groove section 12 are set up to the ceiling cornice 9 and the plinth 10.