SUBSCRIBER'S CIRCUIT TESTING SYSTEM

PURPOSE:To confirm the normalcy of a code decoding circuit in a subscriber's circuit being put in a vacant state, by transmitting a test tone of digital form to the subscriber's circuit through a channel network, after the power down state of the code decoding circuit is cancelled from the outside. CONSTITUTION:In the testing time of a code decoding circuit 23 in a subscriber's circuit 2 being put in the vacant state, a power supplying signal (p) is transmitted to the subscriber's circuit 2, and the power down state of the code decoding circuit 23 is cancelled. Next, the test tone of digital form is transmitted from a test tone generation circuit 4 to the subscriber's circuit 2 through a channel network 3, and the code decoding circuit 23 converts a transmitted test tone of digital form to the one of analog form, and transmits it to two-wire/four-wire conversion circuit 22. By receiving the test tone of digital form by a reception circuit 5, it can be confirmed that the code decoding function of the code decoding circuit 23 in the subscriber's circuit is executed normally.