To provide a dry wood board which prevents the warpage and swell of a foundation material from occurring by only bringing the butt face of a flat wood board material into tight contact with another adjacent flat wood board material and thereby keeping these board materials certainly at a specified interval and can be applied easily to form a flat face part in a short time and with high precision as well as a method for applying the dry wood board to build the flat face part of a structure.

The flat wood board material 12 is used for forming the flat face parts of a structure which are arranged adjacent to each other in such a manner that the width end face 14 sides are mutually butted. In addition, the adjacent both width end face 14 sides of the flat wood board materials 12 have butting faces 18 which come into contact with each other. Further, at least one of the butting faces 18 has a protruding piece 20 which keeps the faces 18 apart by the specified width in a mutually butting state and at the same time, tends to snap when the flat wood board material 12 stretches. Thus it is possible to certainly prevent the warpage and swell of the flat wood board material 12 from occurring following the snapping of the protruding piece 20 due to the stretching of the board material 12 because the board materials 12 are kept apart from each other to the specified width by the protruding piece 20.