An image forming apparatus including: an image forming unit which forms an image; a fixing unit which fixes the image transferred to a printing medium; a power supply which supplies operation power to the fixing unit; a contactless sensor sensing a temperature of the fixing unit and respectively outputting a sensor-sensing voltage and a sensor-compensating voltage; and a contactless-sensing protector which shuts off the power if the sensor-sensing voltage is higher than the sensor-compensating voltage. The fixing unit can be protected from overheating and control error through the contactless-sensing protector for sensing the fixing temperature and shutting off the power.