PURPOSE: To suppress the deviation, wrinkling, etc., of a heat-resisting endless film due to deformation by winding the heat-resisting endless film around the outer peripheral surfaces of a heating member and a film guide member in a slacking state, and driving the film.
CONSTITUTION: The heat-resisting endless belt 2 is wound around the outer peripheral surface of the film guide member 3 and the outer peripheral surface of the heating body 1 in the slack state. Then the heating body 1 is heated, a driving pressure member 6 is driven, and a recording material where a toner image is formed is passed between the driving pressure member 6 and heat- resisting endless film 2. At this time, the heat-resisting endless film 2 is driven by the driving pressure member 6 in the slack state together with a recording material and the toner image is fixed on the recording material with the heat and pressure during this period. Consequently, the fixed film neither deteriorates nor wrinkles and the fixing device which has superior durability is obtained.