An image forming apparatus is used for forming a print image on a color image forming sheet on which a plurality of units is formed in a regular pattern. Each unit is formed of plural color areas for showing one color portion. The image forming apparatus includes a storing device for storing image plotting data showing color-plotted images; a control device for translating the image plotting data into print image data including plural groups of digits corresponding to the color areas in one unit; a detecting device for detecting a position of the color image forming sheet on the image forming apparatus and outputting a detection signal upon detection of the position; and a recording device for selectively covering the plural color areas on the color image forming sheet according to the print image data and the detection signal from the detecting means. Thus, the color-plotted image is produced on the color image forming sheet.