The fixing apparatus of an image forming apparatus has a heating device, a feeding device and control device, wherein in a case of continuously forming images onto the material to be heated, wherein the control device changes the turn-on time ratio in accordance with a size of the material to be heated and determines the feeding timing of the material to be heated fed by said feeding device in accordance with temperature distribution of the heating device in a longitudinal direction of the heating member perpendicular to a conveying direction in which the material to be heated is conveyed. It can suppress the occurrence of wrinkles and can improve a throughput.