To provide a fixing method by which an image surface is not damaged though the temperature of the paper passing part of a fixing roller is measured.

This image forming device is equipped with a passing area temperature detection means 10 detecting the temperature of the surface part of a pressure roller 6 corresponding to a passing area (paper passing part) where recording paper passes between the fixing roller 1 and the pressure roller 6, and a passing area outside temperature detection means 5 detecting the temperature of the surface part of the fixing roller out of the passing area. Then, a heating element for the pressure roller is driven and controlled so that the temperature of the surface of the pressure roller may be the specified one according to the detection signal of the passing area temperature detection means and a heating element for the fixing roller is driven and controlled so that the temperature of the surface of the fixing roller may be the specified one according to the detection signal of the passing area outside temperature detection means. When the detected temperature of the passing area temperature detection means is lower than a specified value because the recording paper passes through the passing area, the control reference being the specified temperature of the heating element for the fixing roller is set to a high temperature range, and the heating element for the fixing roller is driven to be turned on.