To improve a yield and to suppress inverse V segregation generated inside an ingot by preventing casting defect of shrinkage cavity, porocity, etc., mainly formed in ingot upper part in particular for an alloy tool steel.

In the electroslag hot top method, in which a slag 5 is charged above the molten alloy poured in a mold 2 and riser frame 3, the tip part of an electrode 6 is immersed in the slag 5, and the upper part of molten alloy is beated by resistance heat generation, a temp. in the slag 5 is controlled to a temp. having a solid phase rate of molten alloy of 10-50% and kept in the temp. region for a fixed time.