To promote the melting at a steel tapping hole without developing the erosion of tip part, etc., of a nozzle by using a medium slender nozzle set in a wafer-cooling jacket on the upper wall of the steel tapping hole, blowing oxygen gas in a prescribed term and jetting while aiming in the range from the position just below the furnace wall to a specified % of the furnace inner diameter to the furnace center side from the above position at the molten steel surface height position in the furnace.

The nozzle used is the medium slender nozzle having a throat part at the water-cooling type tip end part and the inclining angle of the nozzle is made to be adjustable and it is effectively that the ultrasonic oxygen gas flow formed with the nozzle is jetted while aiming the position just below the furnace wall at the steel tapping hole side and the range from this position to the 25% of the furnace inner diameter to the furnace center side. Since a gap exists just before the nozzle, the effect of rebound oxygen gas is reduced, and the nozzle part and a structural material around the nozzle are not eroded, and while aiming the boundary between the molten steel pool part and unmelting scrap in the furnace, the oxygen gas can be blown, and the melt-down of heated scrap and the stirring of the molten steel can effectively be executed.