PURPOSE: To lower the treatment cost of waste resin without using additional fuel, by providing a combustion resin passage for feeding part of waste resin that has been melted in a melting tank to a resin burner.

CONSTITUTION: Waste resin such as waste agricultural resin film is charged into a melting tank 2, a furnace main body 1 is heated by a heating burner 4, and water is fed into a steam generating pipe 8 by a pump 10. The waste resin is heated by outside heating and also by steam from the steam generating pipe to be melted efficiently. Part of the melted resin is passed through a combustion resin passage 16a to a resin burner 3 where it is burnt. When the resin burner 3 becomes operated in a steady manner, the heating burner 4 is stopped and the apparatus is operated using only the heat from the resin burner 3. Thus as additional fuel is not required, the treating cost of waste gas can be substantially reduced.