PURPOSE: To thin a small picture element obtained by means of dividing a picture element and to make reduction printing possible without the perfect omission of the original original picture element by printing an original picture with the picture elements the number of which is smaller than the (n) specified small elements.

CONSTITUTION: A reduction control part 1 successively converts the picture element P of picture data which is serially inputted into the small picture elements p consisting of the eight prescribed picture elements and outputs them to a page printer part 3 (LBP part) as a signal PRINTDT. An oscillator 2 is a clock oscillator stipulating the printing dot width of the small picture elements p and its clock cycle is decided by the main scanning speed of the page printer part 3. Thus, one picture element of the received original printing picture is divided into the eight small picture elements having 1/8 width and the small picture elements are thinned in accordance with a reduction rate so as to execute printing so that reduction printing in a main scanning direction is made possible without the perfect omission of the original picture element only by using a single clock oscillating source.