according to an embodiment of the invention , an image forming apparatus comprises a fixing unit including : a pair of rollers rotating with a recording sheet holding a toner image interposed therebetween ; a driving motor rotating at least one of the pair of rollers ; a heater being built in at least one of the pair of rollers to heat the roller ; a timer measuring a period of time after starting operation ; and a rotation speed control unit controlling the driving motor so that one of the rollers rotates in a speed higher than a rotation speed under normal conditions until a predetermined time measured by the timer .