The image heating apparatus includes an unit for spacing each of a buck-up member and a pressure roller apart from a flexible belt member which is electrified to generate heat, or heated by a source of heat at start-up, i.e. in a previous stage to heating an image, or an unit for controlling a pressure to decrease a contact area in the direction of the axis of rotation compared with the contact area for a period to heat an image. This can control, as much as possible, heat conduction from the flexible belt which is electrified to generate heat, or heated by the source of heat to the back-up member and the pressure roller at the start-up, i.e. the previous stage to heating an image.