PURPOSE: To discover abnormality in its early stage and thereby to prevent lowering of quality and the like by comparing a heating temperature calculated from a detected air quantity and the amount of fuel supply to a burner with a detected hot air temperature and by displaying the abnormality according to whether or not a comparison value obtained is larger than an allowable temperature difference value set beforehand.

CONSTITUTION: Output signals of an air quantity sensor, a hot air temperature sensor 47, etc., in addition to the ones of mode switches 51 to 54 and setting switches 55 to 57 provided in an operating panel are inputted respectively to a control part of a controller provided inside a burner shell. From the control part, on the other hand, drive signals of circulation system drive motors 19 and 62, a burner, etc., are outputted respectively. In the control part, a heating temperature calculated from a detected air quantity and the amount of fuel supply to the burner is compared with a detected hot air temperature. Abnormality is displayed in a display part 63, as the result, according to whether or not the comparison value is larger than an allowable temperature difference value set beforehand. By this constitution, the abnormality in temperature distribution of a hot air chamber and the abnormality of a fuel supply system are discovered in their early stages and lowering of the quality of dried grain or the like is prevented.