PURPOSE: To improve a drying performance of crop particles by a method wherein an average heating amount during one period or a plurality of periods is compared with a set heating amount and an intermittent combustion is controlled.

CONSTITUTION: Heating amounts K1, K2,...Kn are calculated in response to a surrounding air temperature TA and a drying air temperature TB measured by a surrounding air temperature sensor and a hot air temperature sensor for every predetermined time within an ON-OFF predetermined time of a fuel pump and the like. An average heating amount either one period of ON-OFF of a burner or during N periods is compared with a set heating amount calculated in response to a set drying air temperature and a measured surrounding air temperature TA in reference to an average value of these heating amounts K1, K2,...Kn. Then, if they are different from each other, ON-OFF time of the fuel pump and the like is controlled to be increased or decreased in such a manner that the heating amount may become equal to the set heating amount to cause the average heating amount to be equal to the set heating amount and then the crop particles are dried. The measured drying air temperature is controlled to be increased or decreased to cause the crop particles to be dried.