A fixing apparatus including a flexible belt having a heat generating layer, an outer ring provided on one edge side of the belt and along an outer peripheral surface of the belt, the outer ring being electrically connected to the heat generating layer, an inner ring provided on the one edge side of the belt and along an inner peripheral surface of the belt to face the outer ring through the belt, and a power supply unit that is electrically connected to the outer ring and that feeds power. A difference obtained by subtracting a diameter of the inner ring at a normal temperature from a diameter of the inner ring at a fixing temperature is equivalent to or larger than a difference obtained by subtracting a diameter of the outer ring at the normal temperature from a diameter of the outer ring at the fixing temperature.