PURPOSE: To reduce the cost by giving picture element information in the subscanning direction to an interpolation circuit so as to omit a line memory.

CONSTITUTION: In the printer in which a 1st print mode implementing high resolution print and a 2nd print mode implementing low resolution print are provided, an image forming section 100 uses a page memory 102 to store picture element data by one page with a page memory 102 and plural picture element data (output 302) adjacent to each other in the subscanning direction among picture element data by one page stored in the page memory 102 are sent through plural transmission lines and a print device 200 receives the picture element data (output 302) sent through the plural transmission lines, an interpolation circuit 206 is used to interpolate the data in the case of the 2nd print mode and to make printing and in the case of the 1st print mode, the data are printed not through the interpolation circuit 206.