PURPOSE: To apply the pretreatment such as desulfurization, dephosphorization, etc., to molten iron at high reaction efficiency.

CONSTITUTION: An injection lance 3 is arranged at the excentric position of a molten iron ladle 1 under the condition of directing a discharge port 4 to the center part of the molten iron ladle 1. Treating agent is blown into the molten iron from the discharge port 4 so as to develop stirring flow having larger area ratio of the descending flow zone than the ascending flow zone to the molten metal surface in the molten iron 2. By this method, the descending flow is spread in the wide range and the reaction at the interface of top slag/ metal is promoted by the increase of the interface of the slag/metal and shifting speed at the metal side, and the reaction efficiency is improved.