PURPOSE: To enhance the dimensional stability and to reduce the surface roughness by a method wherein an outer-layer material is arranged and united on the surface and/or the rear surface of the required number of inner-layer materials via a resin-coated laminated sheet.

CONSTITUTION: An outer-layer material is arranged and united on the surface and/or the rear surface of the required number of inner-layer materials via a resin-coated laminated sheet. The resincoated laminated sheet is obtained by piling up, laminating and shaping the required number of resin-impregnated boards which are obtained in such a way that a base material of a woven fabric or a nonwoven fabric composed of an inorganic fiber, an organic synthetic fiber or a natural fiber is impregnated with a resin. By this setup, the dimensional stability is enhanced remarkably and the surface roughness is reduced.