PURPOSE: To eliminate conventional trouble by adding an identification signal identifying automatically an input system at each voice input system to a voice signal in response to the presence of a voice input so as to have only to hear out the identification signal superimposed on the input voice thereby identifying the input voice system.

CONSTITUTION: The voice signal branched from a voice amplifier A1 is inputted to a voice signal detection circuit 1-A, and the voice signal exceeding a required threshold value is outputted as a logical value "1". A differentiation circuit 1-B outputs a rectangular pulse wave of a pulse width T at the leading and trailing of an output waveform of the 1-A. In inputting this output to a gate circuit H2 via an OR gate H3 together with an output signal Fm of a gate circuit H1, the modulation waveform Fm of an oscillator E is obtained only once at a time T from the output H3. In setting each T of differentiation circuits 1-B∼1-n to an integral number of multiple of the T of the differentiation circuit 1-B, the identification signal for a predetermined integral number of multiple is superimposed on the corresponding voice signal at each system just after the leading and trailing of the durated time zone of the input voice signal, when the voice signal is inputted to voice input systems L1∼Ln.