1. An audio teleconferencing apparatus comprising: more than two line interface circuits each connected at its line side to a communication line; and an addition circuit provided for mutually interconnecting together said more than two line interface circuits at their interconnection sides; each of said line interface circuits comprising: line connection means connected to said communication line at said line side for receiving a speech signal from said communication line; voice activity detection means connected to said line connection means for detecting the voice activity of the speech signal received; receiving-speech variable loss means connected to said line connection means for attenuating said received speech signal by a predetermined value when it is detected by said voice activity detection means that said received speech signal is voice non-active; sending-speech variable loss means connected between said interconnection side and said line connection means for attenuating a sending-speech signal applied from said interconnection side by a predetermined value when it is detected by said voice activity detection means that said received speech signal is voice active; and amplification means inserted between said variable loss means and said interconnection side for amplifying said received speech signal attenuated by said received-speech variable loss means, by a predetermined value.