Patent ID: 7489328

Claim:
An image forming apparatus, comprising: a laser-beam scanning unit that deflects a plurality of laser beams modulated by image signals corresponding to a plurality of different colors in a main scanning direction, and irradiates the laser beams to a plurality of image carriers corresponding to the different colors, respectively; a plurality of developing units that visualize latent images formed on the image carriers by irradiation of the laser beams, respectively; a transfer unit that transfers the visualized latent images to a transfer element; a first laser beam detector that detects a first detection time in a predetermined position along a main scanning line of an image carrier to which the laser beam is irradiated; a plurality of second laser beam detectors that detect a second detection time in a position different from the predetermined position along the main scanning line; a time-difference measuring unit that measures a time difference between the first detection time and the second detection time; and a magnification correction controller that corrects magnification in the main scanning direction by changing a timing of the image signal based on the measured time difference, wherein the first laser beam detector and one second laser beam detector of the plurality of second laser beam detectors are provided near the image carrier corresponding to a predetermined color, the magnification correction controller corrects the magnification in the main scanning direction by changing a timing of the image signal corresponding to a color different from the predetermined color, based on the time difference measured for the predetermined color, and when an abnormality occurs in one second laser beam detector of the plurality of second laser beam detectors, the time-difference measuring unit measures the time difference using another second laser beam detector of the plurality of the second laser beam detectors that is normal.