| 摘要 |
A measuring unit measures a time difference between detections of the optical beams by an optical beam detector arranged on either side of an image carrier with respect to a horizontal scanning direction. A magnification correcting unit determines whether a beam spot position adjustment amount corresponding to each of a plurality of developing colors preset by the sub position correcting unit exceeds a threshold preset for each of the plurality of developing colors, and depending on the result of the determination, performs magnification correction of the image by changing a beam spot position interval on a scanning line in units of a line or lines, or by changing a beam spot position interval on a scanning line in units of pixel.
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