To efficiently avoid an error in the connection or switching of a cable due to a user in an environment like a domestic local area network(LAN) to which plural pieces of equipment are connected by an Institute of Electrical and Electric Engineers(IEEE) 1394 serial bus.

In the case of cable configuration, loop detecting parts 7a to 9a read control signals transmitted and received by ports 1-3 and judge the presence/absence of a loop. When a cable constituting the loop exists, loop display parts 7b-9b display the presence of the loop by flickering light emitting diodes 7c-9c provided corresponding to the ports 1-3. From this display, the user can easily recognize the loop part and by pulling one cable from one of displayed ports, the loop can be canceled.