To achieve a structure capable of detecting the rotating speed, and the widthwise position of a fixing belt 100 without providing a sensor separately.

A fixing belt 100 comprises: a resistance heating layer that generates heat by electric conduction, and an electrode 105 that conducts to the resistance heating layer. An insulation part 200 is provided in a part of the periphery of the electrode 105. A power supply member 81 supplies electricity to the resistance heating layer by contacting the periphery of the electrode 105. A voltage detecting part 78 detects an electric conduction state between the power supply member 81 and the insulation part 200, thereby detecting the contact of the power supply member 81 with the insulation part 200. Since the contact of the power supply member 81 with the insulation part 200 provided in the part of the periphery of the electrode 105 is detected in such a manner, the rotating speed and widthwise position of the fixing belt 100 can be detected without providing a sensor separately.