An image forming apparatus includes a fixing unit, a power supply switch, a timer unit, a backup memory, and a controller. The backup memory is configured to nonvolatilely store an accumulated time, the accumulated time being a total period of time during which a heater is energized for detection of disconnection of a temperature-detecting unit after the power supply switch is turned on. The controller is configured to: recognize temperature of a heated member based on an output from the temperature-detecting unit, control the energization of the heater, and start the energization of the heater when the power supply switch is turned on. The controller is configured to determine that a disconnection of the temperature-detecting unit has occurred if the temperature recognized based on the output from the temperature-detecting unit remains in a predetermined low-temperature zone when the accumulated time has become a predetermined detecting-execution time period.