PURPOSE: To provide the private branch of exchange system offering high service performance in which incoming calls are processed quickly.

CONSTITUTION: The telephone system is built up by using a private branch of exchange to which an information processing unit 12, a radio telephone repeater 16, and an exit/entrance use radio telephone repeater 18 are connected and using a portable radio telephone set 20. Every time the telephone set 20 passes through an entrance/exit 30, the telephone set 20 receives an identification number by a command from the exit/entrance use radio telephone repeater 18 and the identification number is recorded in an information processing unit via the exchange and updated. Thus, whether or not the telephone set 20 registered in the information processing unit 12 is resident in a premises 1 is discriminated instantaneously by the operator or the exchange 10 and the call connection is processed thereby to realize the private branch of exchange system offering high service performance.