PURPOSE: To raise molten steel temp. for compensating the lowering of the molten steel temp. caused by blowing a desulfurizing agent onto the molten steel during RH degassing treatment from a top-blowing lance.

CONSTITUTION: An excess Al for deoxidation over the aimed quantity is added beforehand into the molten steel 4 in a ladle 3 and on the other hand, after executing desulfurizing treatment by blowing the desulfurizing agent 7 onto the molten steel 4 in the degassing vessel 1 from the top-blowing lance 2, oxygen is blown from the top-blowing lance 2 to oxidize Al in the molten steel 4 and the temp. of the molten steel 4 is raised to compensate the lowering of the molten steel temp. caused by the addition of the desulfurizing agent.