Abstract: An apparatus for controlling the temperature of a heat roller comprises an infrared thermal sensor unit disposed in close vicinity to the heat roller and including a pyroelectric infrared thermal sensor, a chopper mechanism and a reference thermal sensor, a signal composing device which composes voltage signals produced from the pyroelectric thermal sensor and the reference thermal sensor, a setting signal generating device which produces a signal representing a setting temperature of the heat roller, a comparing device which compares the setting signal provided by the setting signal generating device with the output signal of the composing devices, a control device which controls power supply to a heater of the heat roller in response to the output signal of the comparing device, and setting signal shift device which causes the setting signal from the setting signal generating device to shift during a period after power of the apparatus has been turned on until the output of the reference thermal sensor sett