PURPOSE: To attain the changeover of a talking and data communication while the mobile body communication equipment and the network controller are being connected by connecting or disconnecting a microphone which transduces a voice into a signal and inputting the signal onto a signal line between a mobile body communication equipment and a network controller to/from the handset depending on the presence of communication data.

CONSTITUTION: A speaker 34 is used to process a signal on a signal line at the speaker side into a voice. A microphone 35 processes a voice into a signal and inputs the signal to a signal line of a microphone side. A tone detector 38 detects the presence of communication protocol data by a facsimile equipment 22 on the signal line at the speaker side and the microphone side. When the protocol data are detected, a relay 39 disconnects the microphone 39 from the signal line and when no protocol data are detected, the relay 39 connects the microphone 35 to the signal line. The externally mounted handset 31 is inserted between a portable telephone set 21 being a communication terminal equipment and an NCU 21, and the externally mounted handset 31 relays the signal line at the speaker side and the microphone side connecting to speaker/microphone terminals.