PURPOSE: To decrease the consumption of a carbonaceous material in the stage of refining a molten steel by using an arc furnace by estimating the reduction condition of the iron oxide in slag and the content of C in the molten steel in accordance with the transition of a waste gas temp. and blowing the carbonaceous material into the molten steel under prescribed conditions.

CONSTITUTION: The molten steel is subjected to O2 blow to blow gaseous O2 or air enriched with O2 into the steel to increase quickly the temp. of the molten steel. C injection to blow the carbonaceous material to the molten steel while the O2 blow is continued is then executed. Such injection is started at ≤60wt% content of the iron oxide in the slag and is executed under the conditions of ≤0.8 O2/C (Nm3/min)/(kg/min) by estimating the reduction condition of the iron oxide in the slag and the content of C in the molten steel in accordance with the transition of the waste gas temp. from the arc furnace. The iron oxide formed by the O2 blow is partly reduced and the content of C in the molten steel is increased up to the prescribed level.