To eliminate the possibility of generating trouble due to sucking scrap by a method wherein a discharging port, connected to a flue, is opened on the side wall of a preheating chamber while a lattice type ventilating door is interposed near the discharging port.

A discharging port 23, connected to a flue 21, is opened on one side wall of a preheating chamber 10. A narrow width bag type door guide 24 is provided near the discharging port 23 of a slanted part 22, extending obliquely upward from the discharging port 23, while a lattice type ventilating door 25 is hang by a wire 26 so as to be free of moving in-and-out of the door guide 24. The ventilating door 25 is provided to prevent the free passing of the scrap through the flue 21 while the scrap, precluded to flow into the flue, can be returned into the preheating chamber 10 along an inclination by the self weight. As a result, the possibility of the flowing of the scrap into a deodorizing tower or a cooling tower and the generation of troubles can be eliminated whereby the maintenance of an electric furnace can be facilitated.