PURPOSE: To improve the telephone service by registering the own telephone number from a telephone set of a new address so as to transfer an external incoming telephone call to a telephone set of the new address automatically.

CONSTITUTION: A special number is provided in the inside of an exchange 10 at first, the user calls this specific number from a telephone set A of the destination transfer so as to register the telephone number of the own telephone set B. Then the exchange 10 calls the specific number when a telephone call comes to the set B, identifies the telephone number of the telephone set A so as to compare the telephone numbers registered by the users. Thus, calls to the set B are thereafter all transferred automatically in the route of B to A. That is, since the own telephone number is registered from the telephone set of the new address, even if the telephone number or the like of the new address is unknown, the incoming telephone is automatically transferred to the telephone set of the new address thereby improving the telephone service.