PURPOSE: To prevent the deformation of a plate material before being placed on a pallet and deterioration of its surface properties by extruding a material composed mainly of a hydraulic inorganic material, cutting the same into a shape smaller to a certain extent than a product panel, and then embedding a reinforcing plate at the bottom immediately and carrying the material as it is to the following process.

CONSTITUTION: An extruded material composed mainly of a hydraulic material is extruded onto a roller conveyor 15 as a belt-shaped plate material 12 and transferred therefrom. During the transfer, the material is cut into a flat material 18, a little smaller than the product panel, by a cutter 17a. The plate material 18 is grasped by a vacuum lift 22a, overlapped on a reinforcing plate 21 and then pushed in. For example, a large number of projections are formed on the reinforcing plate 21, and the plate material 18 before being hadened is bitten into the projections and integrated therein. A reinforcing plate material 23 thus manufactured is carried, and compression finish molding is carried out to stretch the plate material 18 to the given dimension. The molded product is mounted on a pallet. The deformation of the plate material 18 and crackes, creases on the surface and the like can be prevented by said arrangement.