PURPOSE: To prevent an overcurrent load on a power source by determining and controlling the feasibility or not of the power source from the state of a power source system to respective image forming devices to prevent the overloading of the power source system when the sum total of the max. rated current consumption of the image forming devices exceeds the permissible current of the power source system.

CONSTITUTION: The parts exclusive of a heat roll from an electrophotographic device 31 are energized if the power source 34 is turned on. A controller 35 measures the voltage of the power source 34 when there is request for the energization from the heat roll of the device 31. A switch 36 is closed to energize the heat roll of the device 31 if this value is above a certain value. The heat roll of the device 32 is similarly energized. The controller 35 measures the voltage of the power source 34 if there is the request for the energization from the heat roll of the device 33. A switch 38 is held open and the energization is delayed as this value is smaller than the certain value. The power source is prevented from being put into the state of the overcurrent even if the total sum of the max. ratings of the respective devices exceeds the permis sible current of the power source system and attains the connectable state.