To prevent rounding in a longitudinal direction by bonding a divided upper base panel piece to lower plywood so that the fiber direction thereof is turned toward the short direction of the lower plywood to produce a base panel and bonding decorative veneer of which the fiber direction is turned toward a longitudinal direction to the upper surface of the base panel.

The length in the short direction of the upper veneer of upper plywood 12 is made equal to the length L in the short direction of lower plywood 15 and the length in the longitudinal direction thereof is made equal to the length nL in the longitudinal direction of the lower plywood 15 and the fiber direction thereof is turned in the longitudinal direction. Herein, (n) is an integer. The upper plywood 12 is divided at the interval equal to the length L in the short direction of the lower plywood in parallel to the short direction. The upper plywood pieces 12A, 12B thus divided are bonded to the lower plywood so that the fiber direction is turned toward the short direction of the lower plywood 15 to produce a base panel 17. Decorative veneer of which the fiber direction is turned toward a longitudinal direction is bonded to the upper surface of the base panel 17. By this constitution, upper veneer 13 can be made thin and production cost can be reduced.