In case a fixing speed is lower than a transferring speed, the individual conveyor units are controlled such that, while a downstream conveyor unit (61) is conveying a sheet (S1) being fixed at the same speed (V2) as the fixing speed, an upstream conveyor unit (60) may convey the succeeding sheet (S2) at the same speed (V1) as the transferring speed. As a result, the spacing of the two sheets in a fixing unit (9) can be sufficiently narrowed to improve the image forming efficiency. Moreover, the transferring speed need not be decelerated according to the fixing speed. It is, therefore, possible to prevent the deterioration in the image quality and to shorten the image forming time period of the first sheet.