PURPOSE: To make easy the confirmation of set of channel, by listening a signal tone transmitted from one end of two-channel type line formed with an exchanger, with a receiver connected to another end.

CONSTITUTION: An incoming trunk ICT-2 is contained in a test device MTF via a test adaptor TA. Further, an outgoing trunk OGT is contained in the MTF via an auxiliary test adaptor TAA. When an incoming call from a relay line L1 requests the connection to a relay line L2, a channel via the incoming trunk ICT-2, path in a switch frame LLF and an outgoing trunk OGT-2 is formed. When a response key A is operated in the device MTF to confirm the set of channel, a signal tone source DT is connected to the outgoing trunk OGT-2 via the key A and the device TAA. If the channel is normally set, the signal is transmitted to a test handset T.