To reduce the incidence of dimensional variation or warp by bonding and joining a medium duty fiber board to a wooden base consisting of a plywood or veneer laminated material with a non-water soluble adhesive.

A non-water soluble adhesive 12 is applied to a wooden base 11 and then, a medium duty fiber board 13 is placed on the adhesive 12 and further is compressed to obtain a composite board 10. When the non-water soluble adhesive 12 is of the normal temperature setting type, heating is particularly not required. However, when the adhesive 12 is of the thermosetting type, the adhesive 12 is heated at a specified temperature. In addition, the time required for clamping by press has to be time to be spent until the adhesive to be used is apparently set. Thus the medium duty fiber board 13 is joined to the wooden base 11 with the non-water soluble adhesive 12, so that no moisture migration from the non-water soluble adhesive 12 to the wooden base 11 and the medium duty fiber board 13 occurs at the time of pressing. Consequently, it is possible to prevent warp or dimensional variation from occurring.