PURPOSE: To surely connect a caller to an extension subscriber and to prevent undesired confusion between a reply party and the caller by transferring the call automatically to other extension subscribers in the extension representative group when the extension subscriber is called and the subscriber does not reply the call.

CONSTITUTION: When a call comes to an incoming trunk 8 and am extension representative number for extension subscribers 1-3 is received, a central processing unit 5 accesses a storage device to read the information of the extension representative group thereby checking the idle state of the extension subscriber 1. When the extension subscriber 1 does not reply the call and a no response information time elapses by the time limit monitor of a timer 7, the central processing unit 5 checks the idle/busy state of the succeeding extension subscriber 2 and sends the call signal to the extension subscriber 2 when the extension subscriber 2 is idle to stop the transmission of the call signal to the extension subscriber 1.