To obtain a sufficient humidity adjusting effect and a divergent effect of the scent of natural Japanese cedars as their features and to avoid the occurrence of dew condensation and fungi; to obtain sufficient heat insulating effect and sound insulation effect; to make the work easier and reduce manhour and construction cost; and further secure a sufficient strength against loads.

When building a wall W 2, located at a lower position W between a sill 2 (including a beam located below) and a beam 3 located at a higher position, the natural Japanese cedars are used at an inner position of a facing surface 4 constituting the wall W between the sill 2 and the beam 3; and a core wall surface Wm is built by using a thick board B with its thickness Lt selected almost to 2 to 4 [cm]; also when building the roof R by using roof sheathing 6u..., 6d...and rafters 7..., the top side roof sheathing 6u...is applied on the top surface of the rafters 7...; the natural Japanese cedars are used on the bottom surface of the rafters 7...; and then lower-side roof sheathing 6d...of thick board B...selected with the thickness Lt to almost 2 to 4 [cm] is installed.