A heating roller includes an exterior aluminum pipe preferably coated with a Teflon layer. A primer layer is disposed inside the exterior aluminum pipe. An outer insulating layer is disposed inside the primer layer. A heating coil is disposed inside the outer insulating layer. An inner insulating layer is disposed inside the heating coil. An aluminum interior pipe is disposed inside the inner insulating layer, and has a predetermined expandability. The heating roller is used as an image fixing unit for fixing a developed image on a recording medium while being pressed by a pressing roller at a predetermined pressure.