NOVELTY - The treatment tank (1) contains microorganism carrier (4), a stirrer (18) with protruding blade (21) on a rotating shaft (20) for mixing the organic substance under process with the carrier and a heater to heat the tank. Two temperature sensors (Si,So) for detecting the temperature inside the tank and outer atmosphere, are attached to the stirrer shaft and inlet suction port (12) of air, respectively.    DETAILED DESCRIPTION - The controller (28) for controlling the heating of organic substance treatment tank, works based on the output of temperature sensors (Si,So) detecting temperature inside tank and outside air. If the temperature inside the tank is lesser than the external air temperature by more than a predetermined first setting, continuous heating of tank is carried out. If the tank temperature is higher than external air temperature by more than the first setting but less than the predetermined second setting, intermittent tank heating is carried out. If the tank temperature is higher than external air temperature by more than the second setting, heating of the tank is stopped.    USE -   For microbial decomposition of organic substances such as organic refuse, etc.    ADVANTAGE -   Since the tank temperature sensor is attached to the stirrer shaft well immersed in the substance under process, the temperature of the substance at any stage of processing can be correctly detected. Since the controller uses the output of tank temperature sensor for heating control, any heat releases to fermentation can also taken into account for heat control, leading to optimum process heating and considerable energy saving. Since the stirrer shaft performs few relative movements, the contact shock experienced by carrier or the organic substance is small. By taking into account the temperature of external air for heating control, the controller performance increases. DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional view of the organic substance processing installation. (1) Treatment tank; (4) Microorganism carrier; (12) Inlet suction port; (18) Stirrer; ; (20) Rotating shaft; (21) Protrusion blade; (28) Controller; (Si,So) Temperature sensors.