PURPOSE: To prevent imposition of a talking charge even onto extension talking as well as external line talking at the introduction of an ISDN line by realizing extension talking between plural ISDN terminal equipments on the same subscriber line not via an ISDN exchange in a station housing.

CONSTITUTION: The system is provided with plural ISDN terminal equipments 1, 2 connecting to one and same subscriber line 3, a line terminator 6 interposed between the subscriber line and a transmission line 7 of an ISDN exchange 8, and a subscriber's exchange connecting an incoming signal of the subscriber line 3 in a loopback way in the outgoing direction of the subscriber lien 3 in the case of talking between the said ISDN terminal equipments and connecting an incoming signal of the said subscriber line 3 to the ISDN exchange 8 via the line terminator 6 in other cases.