PURPOSE: To attain both the quality of character void and the uniformity mediate gradation by forming exposure area data and exposure intensity data to be increased reversely proportionally and correspondingly to the density of image data in each pixel and forming a laser drive signal based upon both data.

CONSTITUTION: An LUT 3 outputs exposure area pulse forming exposure area data Y1 reversely proportional to the density of image data (1) outputted from an image data storing part 1. On the other hand, an LUT 5 outputs exposure intensity data Y2 to be increased correspondingly to the density value of the data (1) and a PWM circuit 4 outputs an exposure area pulse (4) obtained by modulating the pulse width of a pixel clock period in accordance with the data Y1. A data register 6 outputs the data Y2 only for the output period of the pulse (4) and a DAC 7 D/A converts the output of the register 6 and outputs the converted result to an optical power modulator such as an AOM to control laser power. Consequently the quality of character void and the uniformity of intermediate gradation can be attained.