An image forming apparatus that can maintain the accuracy of temperature control of an object to be heated within a predetermined range and avoid adverse effects of contamination of first temperature detection means. The image forming apparatus 1 has a photosensitive drum 14, a heater 901, a thermopile temperature sensor 902, a non-contact thermistor 903, and a control circuit 904. The control circuit 904 controls the heater 901 based on an output signal 902s in a case where the output signal 902s is output earlier in time than the output signal 903s, and informs of a state of the thermopile temperature sensor 902 in a case where the output signal 903s is output earlier in time than the output signal 902s.