This invention provides an image processing system which is built by connecting a host device which reads out and executes program data stored in a storage medium, and a device added with a card device function, and which allows easy device connection and has high convenience. In this system, the device connected to the system has a communication controller (11) for controlling a communication between the host device and the device, a card interface (31) for connecting a card device, a card controller (30, 40) for controlling a card device which is detachably connectable to the card interface, a communication unit (2, 3) for sharing device information between the host device and the card device via the card controller and the communication controller, and a controller (10) for allowing another device connected via the card device to use information shared by the communication unit.