PURPOSE: To obtain an articulate playback sound in the opposite conference room by summing up and sending sent signals of plural expanders, compressing the level variation and distributing a received signal from the opposite party, and superposing the signal distributed from a speech sending circuit upon it.

CONSTITUTION: When voicing is carried out in a zone A, a sent signal SA arrives at an expander 1A correspondingly and a signal SB generated owing to the extension of the voice from the zone A to a zone B also arrives at an expander 1B. The difference between the mean level of sent signal of zones during transmission and the mean level of sent signals of zones during nontransmission increases up to the expansion ratio of the expanders 1 after being passed through the expanders 1. Consequently, the sent signals of the zones during the transmission are emphasized in the sent signal of a adder 2 and the sent signal of the zones during the nontransmission are suppressed. A compressor 3 performs amplification while the emphasis of the level difference between the sent signal is maintained, and a sent signal S wherein a signal having a higher level between the sent signals SA and SB of both zones is emphasized and the other lower-level signal is suppressed is obtained. Consequently, the articulate playback sound is obtained in the opposite conference room.