PURPOSE: To reduce lines to transfer conference information mainly such as a voice between a conference device terminal and a switching device by setting the up line of a bidirectional multiple connecting means each time a speaking request is generated from each conference terminal.

CONSTITUTION: That a simultaneously speaking person is one person in an ordinary conference is paid attention to, a competing control is executed for each speaking request, and the up line of the bidirectional multiple connecting means is set to one conference terminal to be decided for each decision. Namely, the conference information transmitted from a conference information transmitting means 54 of a conference device terminal 50 is switched by a line switching means 41 of a digital switching device 40 and transmitted to each conference terminal 60. Each conference terminal 60 receives the conference information by each conference information receiving means 63. Thus, the number of lines to transfer the conference information between the conference device terminal and digital switching device can be reduced.