An image forming apparatus according to the present invention includes: a fixing part having a heater; a control part controlling ON/OFF of power distribution to the heater; a power source part generating a voltage for driving the control part; a main switch for turning ON/OFF power supply from outside to the power source part; and an interrupt signal generation part generating a periodical interrupt signal. The control part, based on the interrupt signal, controls ON/OFF of the power distribution to the heater, turns OFF power supply to the heater upon passage of predetermined time since disappearance of the interrupt signal, and judges that an error has occurred, when the control part is still driving after passage of driving stop time from when the main switch is turned OFF to when the control part stops its driving since the disappearance of the interrupt signal.