To easily and speedily discover a fault position on a switching network by specifying a fault on a transmission line between arbitrary communication terminals in a short time without requiring much work and experiences.

An instruction for displaying displays provided at ATM communication equipment and an ATM transmission line is transmitted from an ATM exchange 4 to an ATM terminal #2. Communication equipment 6 and 7 with a display function and an ATM transmission line 9 receive that instruction and automatically activate light emitters 14-16. As a result, the displays installed at the communication equipment 6 and 7 provided on a transmission route between the ATM exchange 4 and the ATM terminal #2 and at the ATM transmission line 9 display the transmission route through which the relevant display instruction is transmitted. By visually confirming the display of this transmission route, a fault position on a switching network can be located more easily and speedily than visual watching.