PURPOSE: To secure a proper height of an electrode without receiving effects of current control by a thyrister of a power source to prevent reduction of productivity by providing separate control systems for control of arc current and adjustment of the height of the electrode.

CONSTITUTION: A source AC voltage-reduced at a transformer Tr is changed into DC at a thyrister THY to go through a DC reactor DCL, while an arc current between electrodes E1 and E2 is controlled to be constant. In the meanwhile, a voltage between the furnace bottom of an electric furnace F and the upper electrode E2 goes through a voltage converter VT to be compared with a set voltage at a voltage setter VR, and a motor control device D for a drive motor M for the electrode E2 is controlled to eliminate the deviation to zero at an adjuster C. The height of the electrode between the electrode and the furnace bottom is kept proper by this voltage control separately from control of an arc current, so incompliance of molten pool to component specifications, damage to the lining of furnace walls, reduction of an electric power consumption rate, and other reduction of productivity caused by an excessive temperature rise can be prevented.