An exchange capable of increasing the number of participants in a
conference without increasing conference circuits for conference
communications. The exchange (2) switches connections either between a
line wire (11) and a plurality of extensions (10a) to (10c) or between
plural extensions and plural line wires. The exchange (2) comprises: a
memory (27) registered with plural telephone numbers grouped; and a
controller (26) which is notified of a demand of the conference
communications from an extension telephone (3a) connected with the
extensions (10a) to (10c), for acquiring other telephone numbers of the
same group of the telephone number of the extension telephone (3a)
thereby to form a channel for unidirectional communications, and which is
notified of a demand from the extension telephone (3a) for bidirectional
communications with the telephone selected from the other telephones in
the unidirectional communications, for forming a channel so that the
unidirectional communications with the telephone of the selected
telephone number may be the bidirectional communications.