The present invention relates to a fixing apparatus which radiates rays to a detection object and which detects the rays returned from the detection object to obtain a temperature signal. The apparatus specifies a radiant ratio of the surface of the detection object using at least one of accumulated image forming times, detection position, and radiation deterioration, corrects the detected temperature signal based on the specified radiant ratio of the surface of the detection object to produce temperature data, and controls a power to be supplied to a heating mechanism which raises temperature of the detection object based on the produced temperature data.