In an image output control system of the invention, an image processing device makes image data subjected to a preset series of image processing and supplies processed image data to an image output device to output a resulting processed image. The image processing device collects a predetermined number of plural pixels among a large number of pixels constituting the image to one pixel group, specifies number of dots to be created in the pixel group, and outputs dot number data representing the specified number of dots to be created in the pixel group to the image output device. The image output device stores multiple priority orders of pixels for dot formation in each pixel group. The image output device receives the output dot number data, selects one priority order among the stored multiple priority orders, determines position of each dot-on pixel in each pixel group, and actually creates a dot at the determined position of each dot-on pixel, so as to output a resulting image. In the image output control system of the invention, the image processing device supplies the dot number data to the image output device. Even when an image includes a large number of pixels, this arrangement ensures quick data supply and thereby high-speed image output.