A fixing apparatus includes an external heating device which has a halogen lamp and is disposed on the outer surface of a fixing member so that a nip area is provided between the external heating device and the fixing member. A temperature difference between a surface temperature of the external heating device and a surface temperature of the fixing member is controlled in accordance with a length of the nip area in a direction of transport of the recording paper, so that the surface temperature of the fixing roller is maintained to fall within a temperature range in which offset does not occur, the offset being a phenomenon in which part of a toner formed on the recording paper sticks onto the surface of the fixing roller.