A heating roller is constituted by an elastic roller AA in which an elastic thermal insulation layer is formed, and an endless cylindrical member BB in which a releasing layer is formed on a thin-film base material (heat generating layer), wherein the elastic roller AA and the cylindrical member BB are constituted such that they are separable, and wherein a slight gap is formed between the elastic roller AA and the cylindrical member BB. Then, when a fixing device is started up and the heating roller is rotated, a deflection B1 of the cylindrical member BB caused by the inner diameter difference between the cylindrical member BB and the elastic roller AA is generated on the paper entry side.