To make the replacement of interior finishes easier by forming the interior finishes with decorative sheets having flexibility and arranging them to curved shapes by the flexibility of this decorative sheet.

Ceiling work is carried out by using an elastic coupling device 2 installed at the side surface near the ceiling of columns 311, 312, an elastic coupling device 2 provided at the strut 327 and two flexible decorative sheets 10. And the length of a decorative sheet 10 arranged between a column 311 and a strut 327 is made longer than the distance between the column 311 and the strut 327 and also formed to a pre-curved state by the flexibility. In addition, a lighting fixture 801 is provided at the tie beam 324, a lighting fixture 802 is provided between the tie beam 324 and the columns 311, 312 and the decorative sheet 10 is lighted from the rear side, and the decorative sheet 10 is made by impregnating a resin to a Japanese paper. Thus, the interior finishes with excellent design can be obtained together with light weight and easy installation work.