PURPOSE: To perform stable operation over a long period of time by arranging a furnace bottom plate and the base of a furnace bottom electrode by providing a space horizontally or vertically or horizontally and vertically and mounting an insulating part on the support part of the furnace bottom electrode outside a furnace.

CONSTITUTION: A furnace bottom electrode is constituted of the rod-shaped electrodes 11 mounted on a conductive plate 1 and the rod-shaped electrodes are mounted on the base of the furnace bottom electrode and a current is supplied to the conductive plate 1 from a feeder cable 4. The furnace bottom electrode is arranged by providing a space 6 between a furnace bottom plate 5 and the base 3 of the furnace bottom electrode and fixed by the support device 8 provided to the furnace bottom plate 5 through an insulating material 7 and molded refractory 10 is arranged to the upper part of the space 6 in order to prevent the falling of the stamp material 9 of a furnace bottom from the space 6. Even when lead in scrap begins to accumulate on the bottom part of a furnace during the continuation of operation, lead flows out of the space provided between the furnace bottom plate and the base of the furnace bottom electrode.