PURPOSE: To improve an electrode life by providing a cooling box inside a bar electrode so that the cooling box may be moved to an optional position inside the bar electrode.

CONSTITUTION: The furnace bottom of an electric furnace is lined with a refractory 1, and the outer side is supported with an iron shell 2. A steel-made bar electrode 3 penetrats a furnace wall, composed of these iron shell 1 and refractory 1, to be mounted on the furnace bottom. A copper-made cooling box 4 is mounted inside the electrode 3, a refrigerant 5 such as water is supplied to and discharged from the cavity part inside the cooling box 4, and heat from the electrode 3 is taken out by the refrigerant 5. When a drive device 6, such as a hydraulic cylinder for moving the cooling box 4 in the inside of the electrode 3 is arranged, the device 6 is fitted to a supporting base 7 fixed to the iron shell 2, etc., and the position of the cooling box 4 can be moved according to the wear and tear condition of the refractory 1.