PURPOSE: To make a specific extension receive transmission to an originating call trunk line control dial by registering by conforming the originating call trunk line control dial to an incoming call destination number, collating a trunk sending dial with a registered origination call trunk line control dial, and starting a trunk line when coincidence is obtained between them.

CONSTITUTION: When a subscriber A who uses a subscriber terminal 1 transmits a the trunk sending dial D1, a processor 5 captures the trunk line. and writes the trunk sending dial D1 on a trunk sending dial accumulation part 61. Furthermore, the processor transmits the trunk sending dial D1 by sending to the trunk line when the flag Fa of address (a) of a registration information part 62 is set in a non-registering state. When the flag Fa is set in a registering state. it is collated whether or not the dial that coincides with the originating call trunk line control dial D2 in an originating call trunk line control dial registration part 63 exists. When it exists, the trunk line is released, and an incoming call destination signal D3 in accordance with the originating call trunk line control dial D2 is sent to and received by an extension.