To utilize chaff fuel at low costs in air-heating for greenhouse culture, as application of agricultural greenhouse culture in winter is extremely low, and a self-sufficient rate in agricultural production in Japan is low, so the application of agricultural greenhouse culture must be promoted.

The chaff inside of a hopper 18 is charged into a fuel supply pipe 7 of a combustion device by using a screw conveyor 21. The chaff is pushed in and brought into contact with the chaff firing in advance at an upper section of a combustion plate 8, thus rice husk charcoal state is formed. Further, the air is taken by allowing the chaff to pass through above an air injecting section a, thus the combustion of the chaff is started. The chaff can be burned as fuel without using auxiliary fuel by providing a gasification process and a combustion process with small times.