An apparatus includes a plurality of light-emitting sources configured to irradiate a photosensitive member in a sub scanning direction with a plurality of light beams scanned in a main scanning direction of the photosensitive member via an optical system, a conversion unit configured to convert image data into pixel data constituting a pattern that expresses a density with a plurality of pixels, and a drive unit configured to cause the plurality of light-emitting sources to emit light based on the converted pixel data, wherein, where a number of light-emitting sources is B and a number of pixels of the pattern in the sub scanning direction is M, the number B and the number M have a relationship such that the number M is not divisible by the number B or the number B is not divisible by the number N.