PURPOSE: To permit economical drying as well as the securing of stabilized quality at all times even when the conditions of granular body and atmosphere are changed by a method wherein a drying temperature is changed and set based on the output signal of a regulating meter except the regulating meter of the drying temperature while the supplying amount of heat source and/or the supplying amount of the granular body are regulated so as to coincide with the set drying temperature.

CONSTITUTION: When the moisture content of dried granular body becomes higher than a set value in a moisture regulating meter 23, the output of the regulating meter 23 sets a drying temperature at a temperature higher than the present set temperature while the set value of the drying temperature is reduced when the moisture content has become smaller than the set value on the contrary. On the other hand, when a difference between the wall surface temperature of a drying device and the dew point of hot exhaust gas, which is detected by a dew point regulating meter 20, is smaller than a set value or the relation of both temperatures is reversed, a dew point regulating meter 20 shifts the set value upward to elevate the drying temperature so as to avoid dewing on the wall surface. On the contrary, when the temperature difference is larger than the set value, the output of the regulating meter 22 shifts the set value so as to reduce the drying temperature. A selector 21 selects higher value between the set drying temperatures outputted from the moisture regulating meter 23 and the dew point regulating meter 20 at all times and outputs the higher value as the set value indicated by a drying temperature regulating meter 19.