An inner heating member is disposed in contact with an inner circumferential surface of a heating belt and an outer heating member is disposed in contact with an outer circumferential surface of the heating belt to heat the heating belt. A restricting member configured to restrict an orbit of the heating belt is disposed between the inner and outer heating members. Then, at least either one of an area of contact between the inner circumferential surface of the heating belt and the inner heating member and an area of contact between the outer circumferential surface of the heating belt and the outer heating member is changed to quickly change a quantity of heat applied to the outer circumferential surface or inner circumferential surface of the heating belt.