PURPOSE: To execute decarbonization of high Cr steel for a short time, by supplying powder containing mainly Cr oxide through a tuyere under the specific condition at the time of supplying inert gas from the tuyere below the molten surface to the Cr-contained steel in a refining furnace.

CONSTITUTION: The Cr-contained molten steel 3 having ≤0.30% C content and floating slag 4 at the upper part is poured in the converter 1 providing a lance 2. And, the tuyeres 5 are arranged below the molten surface in the converter 1 and inert gas, such as Ar, etc., or mixed gas for the inert gas and oxygen gas is supplied. Then, the powder 6 having ≤1mm average grain size and oxides of Cr, Mn, Fe as main component is supplied in the tuyere as a simple substance or mixture at 0.05W1kg/min/ton of molten steel supplying velocity to the molten steel 3. in this way, by using only a little quantity of inert gas, the decarbonization having high economical effect is obtd. for a short time.