PURPOSE: To simplify constitution and to improve operability by performing temperature control and temperature compensation differing in purpose through single temperature detecting element.

CONSTITUTION: The temperature detection output of a temperature detecting element 5, such as a thermistor having negative characteristics, is compared with comparators I2WI4 having the different threshold values and on the basis of comparison results, corresponding relays RA1WRA3, etc., are controlled to perform temperature compensation for temperature control, toner density control, power pack output control, etc., through a cooling fan motor. Since a number of dedicated temperature detecting elements, etc., are unnecessary, the number of parts is decreased and thus while the constitution of the temperature controller is simplified, operability of maintenance administration, etc., is improved.