An image forming apparatus is provided which includes a plurality of optical scanners, each including a rotating polygon mirror adapted to scan and expose a surface of an image bearing medium to create an electrostatic latent image on the surface in accordance with image data; a plurality of phase detectors, each assigned to a respective one of the plurality of optical scanners for detecting rotated phases of the rotating polygon mirrors; and a rotated phase controller configured to control the rotated phases of the rotating polygon mirrors, wherein the rotated phase controller is configured to control the rotated phases of the rotating polygon mirrors in accordance with results of detection by the plurality of rotated phase detectors so that rotated phase relationships of the rotating polygon mirrors are set to a predetermined pattern.