PURPOSE: To improve telephone exchange service by providing an automatic answer by the automatic voice responding device to an overflown call in case when the calls are overflowing at a switchboard and by performing the reserve-service processing for the next call.

CONSTITUTION: When a call arrives at the automatic response-service switchboard, a response signal is transmitted to the switchboard-extension trunk IWT. When the line is connected, the automatic voice answer equipment AVAE announces the overflowing state and the call-back processing by its speech synthesizing function, and requests an originating subscriber to notify his own telephone number and that to be connected. The information notified are accumulated in a number accumulating device MEME, then the automatic voice answer equipment AVAE informs the original subscriber that the reserve service is in wait. Parallel to the above sequence, the exchange interface equipment CIE is monitoring the available/busy status of the exchange CBD, and if it finds the available status after setting the reserve service, the interface equipment CIE makes a request to the available exchange asking the operator for a transmit-connection operation. In the result, at the occurrance of overflowing, the exchange service is improved by the follow-on of the call not connected, and additionally the load of the operator is relieved.