PURPOSE: To prevent the generation of defective casting without increasing the pouring temp. of a molten metal in the stage of precision casting using a metallic pattern by using porous materials to form the thin walled part, round part, other parts where the drop of a molten metal temp. is desired to be averted and part to improve gas ventilation of a casting.

CONSTITUTION: The porous materials 3, 4 having excellent heat insulating property are used for the narrow thin-walled parts between a casting mold and a core mold 2 in the stage of precision casting using a metallic pattern as the casting mold. The porous materials 5, 6 are respectively used for the part where a runner 1a is formed and the part where a riser 1b is formed. A foamed metallic body consisting of Ni having about 70% porosity and about 50 pieces of pores for each 1 inch or press molded and sintered bodies made of metallic powder, metallic fibers, ceramic powder, ceramic fibers, etc. and metallic plate having many vent pores are used for the porous materials. The required thin- walled parts are formed in the thin-walled part, round part and other parts of the casting as the quick cooling in said parts is prevented by the heat insulating property of the porous materials. The generation of defective shape parts is thus prevented.