PURPOSE: To directly refine a steel from iron ore with good thermal efficiency by throwing the iron ore and coal into a bottom blown converter, blowing gaseous oxygen therein and splashing a molten iron and molten slag.

CONSTITUTION: The molten iron 7 is put into the converter 1 and an inert gas such as Ar is blown from bottom tuyeres 5 into the furnace to stir the molten iron 7. The iron ore 9 and coal 10 are charged at the same instant into the furnace from the top and oxygen 11 is fed from tuyeres 15 in the upper part. Part of the coal charged into the converter is burned by the oxygen 11 and heats the furnace inside. The iron ore is reduced by the remaining coal and the formed molten iron enters the inside of the molten iron 7. The CO formed by the reduction reaction is subjected to secondary combustion by O2 to form the combustion forming gas of a high temp. On the other hand, the high-temp. exhaust gas of the furnace is blown into the furnace from tuyeres 14 provided in the middle barrel of the furnace to form mist-like splashes 17 of the molten iron 7, by which the heat of the high-temp. gas in the furnace is absorbed and the molten iron 7 is heated up; at the same time, the molten iron is decarburized and refined by the oxygen 11. The refined iron is continuously discharged as a molten steel from a tap hole 13.