In an image forming machine, density data of small pixels in an objective pixel determined according to density of pixels adjoining the objective pixels, the objective pixel determines a recording position for each color based on density distribution of the adjoining pixels when the recording position of each color is modulated in the primary scanning direction and secondary scanning direction based on density distribution of both the objective pixel and the adjoining pixels. Further, there are provided an image discriminator for image judgment on the objective pixel and a modulator for modulating a recording position using a reference wave with a long cycle when an image is judged to be a halftone image area under a reference wave with a short cycle when an image is judged to be a character image area.