To improve the quality of steel ingot by controlling the slag temperature corresponding to the solid phase ratio of the molten alloy to reduce the reverse V-segregation concentration in performing the electro-hot top in manufacturing the ingot for tool steel represented by high-carbon high-chromium steel.

During the hot top, the slag temperature is controlled so as to obtain the temperature at which the solid phase ratio is 10-50% of the solid phase ratio of the molten alloy 4. An electrode 7 to be dipped at least in the slag 5 in a feeder frame 3 is erected close to an inner wall 6, and after the electrode is kept for the prescribed period in the temperature range, the electrode 7 is moved to a part 6' close to the axis of the feeder frame 3 so that the solid phase ratio at an upper part of the molten metal 4 is in the range of 10-50%. The hot top is applied to alloy tool steel in which ≥0.5% carbon is contained by weight and ≥5% of carbide forming elements in total except carbon is contained in the composition of the molten alloy 4.