PURPOSE: To identify whether a reply comes from a transfer sender or a transfer destination by sending a call tone different from a call tone at transfer destination calling to a caller when an arrived call during talking is transferred and the call returns again to the transfer sender because of no reply of the transfer destination.

CONSTITUTION: A call tone used for calling back again a transfer sender because a transfer destination does not reply for a prescribed time is made different from a call tone when the transfer destination is called. While an extension telephone set 1 and an extension telephone set 2 are busy, when the extension telephone set 2 uses a simple transfer function of an exchange to transfer its call to an extension telephone set 3, a call tone 11 is sent to the extension telephone set 1. Moreover, when the extension telephone set 3 does not give a reply for a prescribed time and the extension telephone set 2 is called back again, a call tone 12 is sent to the extension telephone set 1. Thus, the extension telephone set 1 can identify a call destination based on the two kinds of the call tone. Furthermore, a main storage device 9 is provided with a timer watching no reply of the transfer destination for each of the extension telephone sets 1-3 and with a memory area 10 storing subscriber information of an extension telephone set being a transfer sender.