PURPOSE: To prevent internal segregation and inside surface cracking and to obtain a hollow steel ingot having excellent quality by using a core consisting of a thin-walled metallic cylinder and support provided therein, pouring a molten steel into a casting mold and cooling weakely the molten metal with gas during solidification and cooling forcibly the molten steel with water in the second half of the solidification.

CONSTITUTION: The casting mold 6 and core 8 are imposed on a molding board 2. The core 8 consists of the thin-walled metallic cylinder 14 which is buckled and deformed by the heat of the molten steel 10. The support 16 is provided in said cylinder. The cooling medium such as air is supplied from a piping 18A by a supply pipe 17 to the core 8 to cool slowly the core 8 during the pouring of the molten steel 10 into the mold 6 and in the first half of the solidification. The water 24 is supplied from a piping 18B and supply pipe 17 into the mold in the second half of the solidification to immerse the core 8 in the water 24 by which the core 8 is forcibly cooled. The inside surface of the steel ingot has no segregation line and the good steel ingot having the hollow inside characteristic is obtd. by the above-mentioned method.