PURPOSE: To perform desiliconization, desulfurization and dephosphorization of molten iron in the same vessel by putting the molten iron into the vessel which is segmented to 2 or 3 parts in the surface layer part, and blowing a desiliconizer, a desulfurizer and a dephosphorizer through lances into the respective segments.

CONSTITUTION: Heat resistant partition walls 5, 5 are immersed into the molten iron in a mixer car at immersion depth of ≥20% of the depth of the molten iron, whereby the molten iron surface part is segmented to 3 parts, A, B, C. A lance 1 is immersed in the part A, through the former of which iron oxide or gaseous oxygen is blown to oxidize and desiliconize the Si of the entire molten iron, thereby reducing the content of Si to ≤0.15%. next, a mixture of Na2CO3 + iron oxide or CaO+CaF2+(iron oxide)+CaCl2 is blown as a desulfurizer and a dephosphorizer through a lance 2 immersed in the segment part B to desulfurize and dephosphorize the molten iron to target levels. If it is desired to lowr the contents of S and P in particular, a strong desulfurizer or a strong dephosphorizer such as CaC2 or CaO is blown into the molten iron in the segment part C through a lance 3 simultaneously in parallel with this or after this.