PURPOSE: To manufacture a solid plate for building by mixing rock wool and organic thermoplastic resin to form a porous plate material, heating and melting the organic thermoplastic resin.

CONSTITUTION: Rock wool and organic thermoplastic resin are mixed together to form a porous plate material, and the organic thermoplastic resin is melted and dissolved by heat treatment. Further, a plate for building is manufactured by applying the sheet-making technology of using starch for said structure and the sheet-making technology of adding incombustible fiber, organic insoluble fiber or woody fiber therein. The plate 1 for building thus manufactured can be used as it is, and also can be laminated with a sound insulating sheet 2 or with a rock wool plate 3 for use. Strength is increased by said arrangement, and heat insulating properties, sound absorbing qualities, water resistance and incombustibility can be controlled freely.