A color image forming apparatus is provided with a printer controller which is capable of receiving color image data for one page, which is divided into a plurality of data for each of a corresponding plurality of colors, at an irregular interval, and, upon receiving the image data for one color, driving an image forming device to form an image of the color whose data has been received, and after images of all of the plurality of colors are completed, outputting the final image on a recording media. The image forming device may also include, an intermediate image transfer belt for forming thereupon an image of each of the plurality of colors, superposing one on another, and a leading edge detect sensor to detect a leading edge of an image of each of the plurality of colors for registering the leading edges of images of the plurality of colors. The apparatus may further include, in addition to a scanner and a printer, a system controller which issues an image formation command for each of the plurality of colors to the scanner and the printer at a regular interval in a copy mode, and to the printer at an irregular interval in a print mode.