PURPOSE: To improve the addition yield of Al for alloying by adding and immersing Al into the position under the surface of a molten steel after subjected to decarburizing refining by means of oxygen blowing, carrying out reducing refining while maintaining a low vacuum, and also diffusing Al into the molten steel.

CONSTITUTION: A molten stainless steel is subjected to decarburizing refining by means of oxygen blowing under reduced pressure in a VOD furnace. Metallic Al, reducing agent, and slagging agent are added and immersed under ordinary pressure into the position under the surface of the molten steel after decarburization. Reducing refining is carried out while maintaining the pressure at a low vacuum of ≥40Torr for a sufficient time and also Al is diffused into the molten steel. The added Al functions as a reducing agent for chromium oxide and also an alloying material for producing a high Al stainless steel. By this method, the evaporation and volatilization of metallic Al at the time of refining can be prevented, and the component regulation of Al content in a product can be facilitated.