A channel disconnection detecting unit detects whether a voice channel is disconnected by an AG or by an HF. When the voice channel is disconnected by the AG, an AG control unit controls a modulation/demodulation unit to maintain a connection of the AG with a BS and a switching unit switches a voice signal to an AG speaker and an AG microphone. When the voice channel is disconnected by the HF, the AG control unit controls the modulation/demodulation unit to interrupt the connection of the AG with the BS.