To prevent the sticking of reduced particles to a nozzle by lining a heat insulating material on the outer peripheral part of the nozzle for supplying reducing gas and cooling the outer peripheral part of the heat insulating material to a prescribed temp.

Only by lining the heat insulating material 13 on the nozzle 12 for supplying the reducing gas, the outer surface temp. of the heat insulating material 13 is at the reducing particle temp. or higher and exceeds about 700°C at which the reduced particles have sticking property, consequently, the sticking of the reducing particles to the nozzle 12 can not be prevented. Then, cooling grooves 14 are formed around the heat insulating material 13 and water cooling or air cooling is executed so that the furnace outer shell temp. at the outermost peripheral part of the nozzle 12 in contact with reduced particles becomes ≤700°C.