PURPOSE: To obtain a lightweight molded hardboard having strength by subjecting wood pulp having a phenol resin added thereto to rolling molding and bonding the molded one to the upper and rear surfaces of a plastic foam sheet material before foaming under heating and pressure.

CONSTITUTION: A phenol resin is added to dry wood pulp to be mixed with the pulp by a mixer 13 and the resulting mixture is subjected to calender molding by a forming machine 14 to form a sheet which is, in turn, dried by a dryer 15 to be processed into a wooden mat material 20. The wooden mat materials 20 are laminated to both upper and rear surfaces of a phenol sheet material 21 wherein a non-foamed phenol resin is bonded to a nonwoven fabric by a laminating machine 16 and the whole is heated and pressed by a hot press machine 17 not only to thermally cure the phenol resin in the wooden mat material 20 but also to foam the non-foamed phenol resin of the phenol sheet material 21 under heating to mold a hardboard having a required shape. By this constitution, the thickness of a hardboard layer can be reduced while strength is kept.