To properly lift or lower an electrode invariably under various conditions and stabilize the fed electric power by providing a low-sensitivity zone slowly responding to the fluctuation of impedance in a furnace and lifting or lowering the electrode at a low speed near the stop equilibrium point of the electrode.

The electrode 2 of an arc furnace is supported by an electrode lift device 3 to be suspended in a furnace body 1, and it is lifted or lowered when a motor 4 is operated. A furnace power supply is provided with a circuit breaker 5, a power converter 6 and a programmable sequencer 7 storing a microcomputer. The sequencer 7 monitors the electrode current and electrode voltage applied between the furnace body 1 and the electrode 2, calculates the deviations of the electrode current and electrode voltage, and calculates a speed based on the deviations. The calculated speed is instructed to an inverter unit 8, and the motor 4 is rotated to lift or lower the electrode 2 as instructed.