An image forming apparatus forming toner images sequentially on recording sheets transported at intervals, and thermally fixing the toner images by passing the recording sheets through a fixing position on a heating roller. The target fixing temperature is determined according to information of an image on each page. When a first fixing temperature for a given page is higher than a second fixing temperature for the succeeding page and the difference therebetween is greater than a predefined value, part or all of a first period, during which the thermal fixing operation for the given page is performed, and a second period, which corresponds to an interval between the two pages, are reserved for raising the surface temperature by the difference, and temperature control is performed during the reserved periods such that the surface temperature reaches the second temperature before the thermal fixing operation for the succeeding page starts.