PURPOSE: To prevent the occurrence of corrugation by heating and sticking a sheet material onto the reverse surface of a woody base plate having a plurality of substantially parallel grooves on the reverse surface through a thermally shrinkable sheet.

CONSTITUTION: When a decorative sheet 1 is stuck to the surface of a woody base plate 13, and a plurality of grooves 12 are formed in the longitudinal direction of the bottom surface of the woody base plate 13, the woody base 13 is warped downward in an arch. A thermally shrinkable sheet 14 is stuck to the bottom surface of the woody base plate 13, and a sheet material 15 is stuck to the lower surface of the thermally shrinkable sheet 14 to form a direct sticking floor board 10. When this direct sticking floor board 10 is hot- pressed, the thermally shrinkable sheet 14 is shrunk to pull the woody base plate 13, and the whole direct sticking floor board 10 is warped upward in an arch. When this floor board 10 is put on a floor bed, it flexibly fits the bed by the dead weight. Thus, the occurrence of a thrust between the floor boards can be prevented.