To prevent difference in chromaticity due to variation in characteristics of laser beams when leading edge timing is regulated by changing the writing start position of the laser beams.

In an image forming apparatus, as to leading edge timing regulation values set based on at least information of a paper supply tray or paper accumulated in the paper supply tray, a regulation value of a regulation width covering a set of scanning lines consisting of all the scanning lines scanned and exposed at the same time by an exposure part is assigned for regulation of leading edge timing of an image, and the remaining regulation value of less than the regulation width is assigned for regulation of leading edge timing of the paper. Regulation of the leading edge timing of the image and regulation of the leading edge timing of the paper are carried out based on the individually assigned regulation values.

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