A system comprising a plurality of network-connected private branch exchanges (PBXs), wherein an outside originating route of a transfer source terminal is applied at call incoming from an originating terminal of the other PBX to a transfer source terminal having a setting of an outside incoming call transfer of a user's own PBX. Upon call incoming from an originating terminal to a transfer source terminal, a PBX accommodating the transfer source terminal transmits a transfer instruction signal including transfer information enabling identifying a PBX accommodating an outside line (a public network) of a transfer destination to a PBX accommodating an originating terminal. The transfer instruction signal is made to pass PBXs other than the PBX accommodating the originating terminal. Upon receiving the transfer instruction signal, the PBX accommodating the originating terminal identifies the PBX accommodating the outside line of the transfer destination by analyzing the transfer information and transmits a transfer originating signal. This causes the PBX accommodating the outside line of the transfer destination to originate an outside call to the transfer destination.