PURPOSE: To attain image processing with excellent sharpness, gradation and granuality and a wide dynamic range by scanning a photosensing body through the comparison between a received image signal and a reference signal frequency-modulated depending on a characteristic quantity of the image signal and lighting or extinguishing a laser beam used for exposition.

CONSTITUTION: A received image signal is converted into an analog signal whose amplitude is in a range of -1V to 1V by a D/A converter of a comparator circuit 15 and a comparator of the comparator circuit 15 compares the analog signal with an input (r) from an FM modulation circuit 32. Since an image output device 16 in this case adopts the image writing system making print to a lighting section of a laser, the comparator provides an output of a lighting signal only when the image signal is larger than the input (r) from the FM modulation circuit 32. Thus, a low frequency output is obtained with a low input contrast where gradation is continuously changed and a high frequency output is obtained with a high input contrast such as a character respectively.