PURPOSE: To recover waste gases in the operation of a top and bottom blown converter as waste gases of high calories contg. much CO and H2 by regulating the quantity of the gaseous oxygen to be supplied from the upper part to control the content of CO2 in the waste gases within a specific range and adding carbon materials and hydrous materials in a flue.

CONSTITUTION: The waste gases contg. CO produced in decarburization reaction in the stage of decarburizing and refining molten iron to steel in a top and bottom blown converter 10 are subjected to combustion and evolution of heat of CO by the oxygen through oxygen lances 14-1, 14-2 for acceleration of combustion in the upper part and the heat thereof is transmitted to the molten steel, whereby the thermal efficiency of converter operation is improved and the use ratio of cold material scraps is improved. The combustion of CO is so regulated that the value of CO2/(CO2+CO) as the compsn. of the waste gases produced in this case attains 15W40%. In the stage of discharging the waste gases from a flue, carbon materials such as charcoal powder and steam or the like are added to increase the contents of CO and H2 in the waste gases, whereby the waste gases are recovered as high calory gases of ≤10% CO2.