1. An image forming system which includes an image processing device for processing image data in a predetermined image process, and an image forming device for forming an image based on the image data processed by the image processing device, the image processing device and the image forming device being connected to each other, said image forming system comprising: an attributes judging section for judging whether or not the image data is for business use based on attributes of the image data including at least a ratio of color area in the image data; and an output control section for restricting output operation of the image forming device when the judging section judges that the image data is not for business use based on the attributes of the image data judged by said attributes judging section.