To melt preheated raw material without transferring the raw material, easily implement melting operation, reduce thermal loss of the raw material, reduce melting time, contribute to saving of electric energy required for melting, effectively and economically implement preheating and melting operation of the raw material, make the provision of an additional opening for connecting a duct to an electric furnace unnecessary, eliminating a possibility of secondary air entering the electric furnace and make an exhauster having a high capacity unnecessary in an exhaust gas treating apparatus.

Exhaust gas generated from an electric furnace (A) functioning as a melting furnace is fed to an interior of another electric furnace (B) functioning as a preheating furnace through a duct 1 which makes exhaust outlets of the two furnaces communicate with each other in order to preheat raw material which has been contained in the furnace (B) in advance by the exhaust gas, which is then fed to an exhaust gas treating apparatus through a duct 5 and the like, which is detachably secured to a slag discharging opening B1 provided in the electric furnace (B).