PURPOSE: To decrease the amt. of an inert gas for pressure equalization to be used condiderably and to reduce iron making costs in a blast furnace to be operated under high pressure by utilizing the high pressure of a blast furnace waste gas in the pressure equalizing operation for a pressure equalizing chamber.

CONSTITUTION: The high pressure waste gas from the inside of a blast furnace 7 to be operated under high pressure is supplied through pipings 8a, 8b into a dust catcher 9 and a ring slit washer 10 by which the gas is purified. The purified gas is utilized for power generation for the furnace top. In this case, part of the purified gas from the washer 10 is introduced into an upper bell hopper (pressure equalizing chamber) 3 of the blast furnace to equalize the pressure therein primarily. Since the pressure of the purified gas in this time is made lower than the furnace top pressure by the catcher 9 and the washer 10, the half purified gas under high pressure removed from the intermediate part of the washer 10 is introduced into the chamber 3 to equalize the pressure secondarily. Finally, a small amt. of an inert gas such as N2 is introduced to equalize the pressure in the chamber 3 with the pressure in the furnace inside 7. The amt. of the inert gas to be used is decreased and the iron making costs are reduced.