To improve a thermal efficiency and save fuel when waste material containing organic substances is melted.

A waste material is heated with heated particle thermal medium within a pyrolysis furnace without performing an igniting operation for waste material containing organic substances and a melting operations for melting combustion ashes in separate manner, the generated thermal medium and sludge discharged from the pyrolysis furnace are separated from each other so as to cause thermal medium to be circulated in a heat exchanger and at the same time the generated pyrolysis gas is supplied to the melting furnace and ignited there to melt the combustion ashes, the molten discharged gas is supplied to the heat exchanger, thereby the molten discharged gas and the thermal medium are directly heat exchanged, both of them are separated, the heated thermal medium is circulated in the pyrolysis furnace and also the heat exchanged discharged gas containing organic substances is fed into a discharged gas processing device.