To reduce the unit requirement of desulfurizing agent and the generated amount of slag by bringing molten iron containing dissolved Al into contact with MgO source placed on the bottom part of a vessel to produce Mg, bringing Mg and S in the molten iron into reaction to float/separate the produced MgS.

Natural magnesia briquette is charged into a molten iron ladle 2 to form the MgO source layer 3. Iron scrap is charged thereto to form a solid iron souse layer 5. Further, the crushed chips, etc., of Al scrap is charged on this iron source layer to form an Al source layer 4. When receiving the molten iron ladle 2 through an inclining through 6, the molten iron 7 collides with the Al source layer 4 and the dissolution of Al into the molten iron 7 starts. The melting of the solid iron source layer 5 proceeds according to the rising of the molten iron level, and the solid iron source layer 5 is lost and the molten iron 7 enters into direct contact with the MgO source layer 3. The Mg is produced from the contact interface between the MgO source layer 3 and the molten iron 7 and reacts with S in the molten iron to make MgS: The produced MgS and Al2O3 float up on the bath surface to foam an accumulated layer. Then Al, not contributing to the reaction, is dissolved into the molten iron 7 to prevent resulfurization from the accumulated layer.