PURPOSE: To enable a high pixel density image to be excellently recorded by reducing deterioration of an image quality by controlling while its cost is being prevented from rising.

CONSTITUTION: A pixel data is separated into an odd pixel data and an even pixel data with a serial/parallel converter 91. Pixels are extracted in pairs successively from a tip. By taking a logical product of the odd pixel data and the even pixel data with an AND gate 9, a strong data being at a 'H' level when both of a pair of pixels are 'black' pixels, is generated. Further, by taking an exclusive OR of the odd pixel data and the even pixel data with an exclusive OR gate 94, a weak data being at a 'H' level when only either of a pair of pixels is a 'black' pixel, is generated. Then, a large 'black' pixel is formed at a position where the strong data is at a 'H' level. Further, a small 'black' pixel is respectively formed at a position where the weak data is at a 'H' level.