PURPOSE: To realize a facilitate and inexpensive processing system by providing a method of remembering and controlling terminal information that corresponds to extension terminals of a switch frame, automatic answering device and line circuit which even if connected to this automatic answering device, detects no telephone call.

CONSTITUTION: In initialization, processor 8 reads and analyzes class information on every extension equipment position from telephone-set class information memory 9 and sends out the operation command of relay contact 11 when the telephone set class shows general telephone set 1 or resets the relay contact when automatic answering unit 7. As a result of this processing, line circuit 6 forming a loop invariably never detects a telephone call from automatic answering device 7. When the number of automatic answering device 7 is dialed from extension telephone set 1, central control circuit 8 connects the two via intra-office trunk 4. In case that telephone set 1 is released earlier, processor 8 releases automatic answering device 7.