A device of this invention solely executes a power saving operation without influencing a repeater operation on a serial bus interface to which a plurality of devices are cascade-connected.A device such as a digital camera, printer, or the like, which is cascade-connected using an IEEE1394 serial bus interface, uses an IC prepared by forming both physical and link layers on a single chip. This IC has a port connected to a bus. When a power supply on the bus side is OFF, this port can insulate the bus in DC term. This device transits to a power saving mode such as a sleep mode, suspend mode, shutdown mode, or the like after an elapse of a predetermined wait time. In the shutdown mode, the system power supply of the device is turned off, but the IC can operate by electric power supplied from a cable. With this operation, a signal can be relayed between devices, and a packet for the link layer can be received. Upon receiving a LINK_ON packet, the device is restored from the power saving mode to a normal drive state.