An image forming apparatus such as a printer and a copier has rotating devices such as a drum and a press roller to print an image on a paper sheet while rotating and a paper-transporting mechanism having guide rollers and timing rollers for transporting a paper sheet to these rotary devices, controlled by a control device such that irregularities in the printed images due to fluctuations in the speed of transportation of the paper sheets. The guide rollers may be operated to transport the paper sheet at a faster speed than the paper sheet is transported by the rotary devices such that the paper sheet becomes bent before being delivered to the rotary devices to be printed on. The control may be such that the guide rollers transport the paper sheet while the timing rollers downstream is released from the transportation of paper sheets. The control device may also operate so as to stop the guide rollers when the paper sheet comes to a position where the rotary devices can start transporting it.