PURPOSE: To obtain a picture of high picture quality from picture data mixedly including characters, line drawings and photographs.

CONSTITUTION: Image formation is executed by prescribed resolution in a part attaching importance to resolution and by 1/3 the prescribed resolution in a part attaching importance to gradation in accordance with the attributes of respective parts in an input picture. A printer controller 2 analyzes picture data transmitted from a host 1, checks whether each picture element in the picture data is character/line drawing data or photograph data and outputs the checked result to a printer engine as a PHIMG signal. A signal processing part in the engine 3 generates a pulse width modulation (PWM) signal so that photograph data in the picture data are processed at 200 dpi recording density and character/line drawing data are processed at 600 dpi recording density based upon the PHIMG signal and drives a semiconductor laser to form a latent image on a photosensitive drum.