PURPOSE: To decrease the inclusions remaining in the bottom of a steel ingot and to make the quality of the steel ingot uniform and good by using an oxide film preventing material in common use as a heat insulating material for a heat insulating head part by specifying the casting temp. of a molten steel.

CONSTITUTION: An oxide film preventing material in common use as a heat insulating material for a heat insulating head part is used and the casting temp. of a molten steel is specified at the m.p. or above and in a 75W100°C range. Addition of ≥90% of said material is completed before charging of the molten steel or within 60% of the entire charging time. Said material has no reactivity with the molten steel and therefore a steel ingot having an excellent casting surface is obtd.