To prevent melting of scrap in a preheating furnace by arranging a cooler at an input side of a shaft type preheating furnace in an inclined rotary kiln type scrap preheating furnace and the shaft type furnace at an upper portion of a scrap melting furnace.

One end of an inclined rotary kiln type scrap preheating furnace 2 is connected to an upper portion of a scarp melting furnace 1, and a lower portion of a shaft type second preheating furnace 3 extended longitudinally is continuously provided with its another end. Scrap charged from the upper portion of the furnace 3 is preheated by the furnace 3, then again preheated in the case of passing the furnace 2, and thereafter charged from above the furnace 1 and melted. In this case, an exhaust gas cooler 9 is disposed at an input side of the furnace 3. An oxygen gas concentration and temperature of the exhaust gas are detected before entering the furnace 3, and a cooling water amount of the cooler 9 is controlled to limit to a temperature for melting the scrap in the furnace 3 in response to the oxygen concentration.