PURPOSE: To perform uniform and stable fermentation treatment by detecting the temp. difference between two points differing in vertical directions, regulating the flow of aif feed, and regulating the rate of ventilation according to the fermentation process of deposited layers in such a way that always adequate fermentation is accomplished.

CONSTITUTION: When fermentation is accomplished by ventilating air through deposited layers 2 from below to above, both temp. sensors 3, 4 are approximately the same in temp. in the initial period of fermentation. When the part of the sensor 4 attains the temp. higher than that of the part of the sensor 3 according to its process, a valve 7 for regulating the flow of air feed is opened from a control unit 5, so that the rate of ventilation is increased up to the set value. On the other hand, when the upper part of the layers 2 ataains the temp. higher than that of the lower part, the flow of feed air is decreased or stopped. In this way, the flow of air feed is regulated according to the process of fermentation from the temp. difference between the two different points of the layers 2 by the sensors 3, 4, whereby the efficient fermentation treatment is accomplished.