Abstract: A communication unit utilizes a caller management unit which monitors in-house lines and detects a caller side calling code included in a calling set up message applied at the time of reference. A control unit stores the detected calling code in one memory region of a memory and reads out the stored calling code from the memory region in response to an output request to produce information corresponding to the calling code. The management unit displays the information produced by the control unit. The memory has another memory region for storing a plurality of predetermined calling codes and caller specification information corresponding to each calling code. The control unit stores the detected calling code into the one memory region in response to a non-response detection to reference by the line monitor.