To enable each image forming device to securely receive and output image data by allowing an image processor to start distributing image data packets to a synchronous transfer bus after receiving paper feed completion notices from all image forming devices and also making the image forming devices receive the image data packets and forming images.

A host computer 110 has an image data distributing means which secures a transfer channel and sends data packets and a paper feed completion receiving means. Printers 102 and 103 respectively have image data receiving means, image forming means, and paper feed completion reporting means and inform the host computer 110 of that image forming forms are completely fed. The host computer 110 after receiving paper feed completion reports from all the printers 102 and 103 starts distributing image data packets to the synchronous transfer serial bus and the printers 102 and 103 receives the distributed image data packets and forms images.