PURPOSE: To attain ease of dial operation by constituting a transfer group with plural subscribers and adding a sub-number to the subscriber in said group.

CONSTITUTION: The subscribers A and C organize the transfer group in advance, and the correspondence between the sub-number and the subscriber number is registered in an RAM. When the subscriber A desires to transfer a call to the subscriber C via a main trunk T, the A informs orally the transfer to the C. The subscriber C noticed of the transfer hooks off, and after the C is connected to an ORT, the C dials a transfer request specific number and the sub-number of the subscriber A. The dialed specific number is fetched by a CPU and the subscriber number of the C is stored in the RAM. The CPU executes the transfer processing with the processing program in an ROM. Further, the subscriber A is disconnected from the trunk and the C and the trunk are connected by using the subscriber number of the C stored tentatively, and then the transfer is finished.