A peripheral device cable, connected to a peripheral device, integrally incorporates a subscriber link that is a physical line for transmitting subscriber information in synchronization with a highway clock and a control link that is a physical line for transmitting control data in synchronization with the highway clock. A control data converter controls interfacing between the control data transferred over the control link synchronously with the highway clock and control data that a control unit transmits/receives asynchronously with the highway clock. The subscriber link is connected to a switch.