PURPOSE: To produce easily, safely and surely a composite metallic cast ingot having high quality by coating preliminarily an oxidation preventive agent which is evaporated by the heat of a molten metal on the surface of a cladding material, covering the coated surface thereof with a cover of a material to be expanded by the molten metal and casting the molten metal into a casting mold.

CONSTITUTION: An oxidation preventive agent 2 of NH4BF4, etc. which is evaporated by the heat of a molten metal is coated on the surface of a cladding material 1 and the coated surface is covered via a small space with a cover 3 which consistgs of a mild steel plate or the like to be expended when the plate contacts with the molten metal and is provided with a small hole 4 communicating with the outdoor air in the upper part. Such cladding material is set in a casting mold 5. The molten metal is then charged through the charging hole 7 of a base plate 6. As the molten metal surface rises, the molten metal erodes the cover 3 and enters the inside thereof to evaporate the material 2, thereby forming a reducing atmosphere and blowing away scum 9. If the molten metal is cast at the speed at which the air pressure in the cover 3 is maintained higher by 0.002W1.0atm than the outdoor air pressure, the composite metallic cast ingot having a good adhesive state without any inclusion defect at the clad boundary is surely obtd.