PURPOSE: To economize a network by suppressing the number of removing circuits to be prepared inside the network into any suitable number by inserting and connecting the echo removing circuits only as needed.

CONSTITUTION: When a call setting message containing the request of an echo canceler is originated when originating a call at a terminal 31 in the case of calling between two-wire analog telephone sets 31 and 33, this message is judged by a subscriber exchange 11, when the canceler is required, a subscriber circuit 7, lines 21 and 22 and repeater line 25 are connected, an echo canceler 13 is inserted to the call, and echo on the side of the line 7 is removed. Then, a subscriber exchange 12 also identifies the request, when the canceler is required, a subscriber line 7, lines 23 and 24 and repeater line 25 are connected, a canceler 14 is inserted to a call, echo on the side of the line 8 is erased, and calling with no echo is enabled. In the case of calling between the terminal 31 and a digital telephone set 36, the echo of the terminal 31 is erased by the canceler 13 and no echo is transferred to the terminal 36. Therefore, the exchange 12 does not use the canceler 14 for this call.