To get a high quantity of conducted radiant heat by arranging a plurality of nozzles to blow in combustion improving gas in parallel with the rotary shaft of a rotary kiln, within the plane vertical to the rotary shaft of the rotary kiln.

A plurality of combusting gas blowing-in nozzles 6 are arranged within the plane vertical to the rotary shaft of a rotary kiln 5 as combustion equipment for combusting the combustible gas within exhaust gas efficiently and raising the temperature of the exhaust gas to a high temperature as far as possible within the heat resistant temperature range of a facility. The scrap 8 being the material for dissolution inserted into the rotary kiln 5 is preheated by exhaust gas produced from a fusion furnace 1 while being discharged to the side of the melting furnace 1 together with the rotation of the rotary kiln 5. At that time, the preheating temperature of the scrap can be raised by combusting the combustible gas within the exhaust gas with the combustion improving gas supplied from a nozzle 6 thereby bringing it into high temperature.