To prevent the lower end of a main electrode from being broken during its positioning work in an ash melting furnace.

A cylindrical electrode 24 provided with female screws 23 on inner circumferential surfaces of its both ends is manufactured of a carbon material. A nipple 24 provided with male screws 25 on its both ends is manufactured of a carbon material. A plurality of the electrodes 22 are axially disposed, the males 25 at both ends of the nipple 24 are threadedly engaged with the adjacent females 23 of each electrode 22, respectively, and thereby a main electrode 4a is formed by linking the electrodes 22. Even if the lower end side of the main electrode 4a is worn out by the main electrode 4a mounted to the ash melting furnace as ash melting treatment advances, its center does not take the form of a slenderized shape extending downward unlike a conventional case.