Abstract: In addition to the conventional telephone portion, this telephone apparatus, coupled to a subscriber's (TEL) line coupled to an intercommunication (ICM) line, comprises a modulation circuit for modulating a data signal to have a frq band different from that used in the conventional telephone portion; a demodulation circuit for receiving/demodulating a modulated data signal having that frq band from another telephone apparatus connected to the same ICM line; and a control circuit for effecting communication with the TEL line and generating control data indicative of inhibition of using the TEL line and transmitting it as the data signal toward another telephone apparatus when the user responds a call or demodulation circuit does not receive modulated data signal indicative of inhibition of using the TEL line from another telephone apparatus. A busy tone may be supplied to the user when the user tries to use the TEL line if the control data is received by the demodulation circuit.