An optical scanning device is provided which comprises a laser array which emits laser beams including a number of beams (1, 2, . . . , n) writing a swath of rasters having a laser scanning section which, when an interlaced scanning period i, is set to a natural number between beams which are adjacent in a sub-scanning direction, scans the laser beams emitted from the laser array with the interlaced scanning period i. The laser scanning section can scan the laser beams such that the beam number n and the interlaced scanning period i are relatively prime natural numbers, and n>i. In a first scan, data for raster lines (1, 2, . . . , n) can be selectively associated with a respective first exposure. At a second scan, data for raster lines (i+1, i+2, . . . , n) can be selectively associated with a respective second exposure and data for raster lines (n+1, n+2, . . . , n+i) can be selectively associated with a respective first exposure. The first respective exposure for raster lines (i+1, i+2, . . . , n) is not equal to the respective second exposure for raster lines (i+1, i+2, . . . , n).