Participant terminals which are to be connected to a promoter terminal are configured by speaker terminals which are enabled to perform two-way communication with the promoter terminal, and audience terminals which are enabled to perform one-way communication with the promoter terminal. The connection line number M of participant terminals which are connected to the promoter terminal is set to M=2S+T where S is the number of connected speaker terminals and T is the number of connected audience terminals. As a result, the total amount of communication is suppressed to S.times.(K-1) (K=S+T) as compared with the conventional art in which all participant terminals are configured by speaker terminals.