Abstract: A method of operating an electric arc furnace is disclosed by which an arc electrode provided in an electric arc furnace is supplied with electric power, an electric arc is extended from the arc electrode and raw material in the electric arc furnace is molten by the arc. Before operation of the electric arc furnace, an electric current I satisfying an equationd[Pi/(Pi-Pl-ql)]dI=0is first calculated where Pi is the secondary output of the used arc furnace transformer. Pl is the total ohmic loss of the secondary winding of the transformer and of an electric circuit connecting the secondary of the transformer with the arc electrode, ql is the heat loss of the used electric arc furnace and I is the electric current flowing from the secondary of the transformer to the arc electrode. Next, when electric power is really supplied to the arc electrode from the arc furnace transformer to operate the electric arc furnace, the beforehand obtained electric current is supplied to the arc electrode from the transformer.