Abstract: A PBX (3-a) detected an incoming call arrived at a line trunk (2-a) via a public line network (1), and at the same time, an ACDP (4-a) queues an incoming call arrived in an incoming sequence queue (8-a). In addition, the ACDP (4-a) scans a distribution sequence queue (9-a), and controls an incoming call to be distributed to an extension line that seems to be the most preferable in the extension line group (6-a). On the other hand, an incoming call arrived at the line trunk (2-b) via the public line network (1) is detected by the PBX (3-b) via a leased communication line (7). At the same time, the ACDP (4-b) queues an incoming call in the incoming sequence queue of the extension line group (6-b). In addition, the ACDP (4-b) scans a distribution queue (9-b), and controls the queued incoming call to be distributed to an optimal extension line belong to the extension line group (6-b).