To prevent density irregularities regardless of any group used when a raster line is formed by switching a plurality of groups divided so that nozzles from the first ones to the n-th ones match.

In the printing system 10, a using object group is set by switching a group A and a group B each other for every page while a sheet of recording paper S is carried in a predetermined direction to a line head 22. A fluid is ejected from nozzles which belong to the using object group after density correction is carried out by a correction table corresponding to the using object group. The raster line is thus formed to the sheet of recording paper S. Whichever group is set as the using object group, generation of a density difference is avoided in a plurality of raster lines. Accordingly, density irregularities can be prevented regardless of which group is used.