To perform an efficient and continuous preheating of scraps, further reduce a melting energy origin unit when scraps are melted at a melting furnace and perform a more smooth preheating and feeding of scraps.

In the case that scraps S of melting raw materials are continuously fed into a melting furnace F while being pre-heated, the scraps S are loaded from an upper location of a main body 2 of a slant and rotating rotary kiln. Then, heat transfer is carried out by a scrap pre-heating heat source 5 for supplying heat to scraps S moved in sequence from the upper location of the main body 2 of the rotary kiln toward an inside section of the main body 2 of the rotary kiln and the scraps S are continuously fed into the melting furnace F while being preheated.