PURPOSE: To prevent a core layer from peeling off from other layer or corrosion due to the action of the open air and the like in a composite inorganic plate comprising a core layer and an outer layer in the perimeter thereof by a method wherein the core layer is formed by injecting a material which is extraneous to the outer layer from an opening of the underside under pressure and causing the material to be in a state of extending around the opening of the underside in a direction of the outer perimeter.

CONSTITUTION: A material B 16 and then a material A 17 are successively filled to form 2 layers in the recessed part of a lower mold 11. It is essential that the total filling amount accounts for 60 to 85% of the internal volume of the lower mold 11. An upper mold 10 is caused to descend to clamp the molds, a material C 18 is cast from an inlet 13 and the inside of the upper mold 10 and that of the lower mold 11 are allowed to absorb the moisture of the material A 17, the material B 16 and the material C 18 to mold the material A 17, the material B 16 and the material C 18 into a body within the molds. At this point, the material C 18 penetrates between the material A 17 and the material B 16 and extends right and left within the molds, lifting the material A 17 upward. Next, the molds are released to obtain the composite inorganic molded body having a part C 18 derived from the material C 18 (core layer) which is situated between a part A derived from the material A 17 and a part B 16 derived from the material B 16, extending evenly around the opening of the underside.