PURPOSE: To make a device small-size and light-weight, by constituting the transmission part and the receiving part of the acoustic coupler as independent bodies separately from each other.

CONSTITUTION: The acoustic coupler has receiving part 7 incorporating microphone 17, sensor 18, and so on and transmission part 6 incorporating speaker 19, and these parts are constituted independently of each other as independent bodies. Receiving part 7 and transmission part 6 are to be mounted in the receiver side and the transmitter side of handset 5 respectively and can be fitted and removed and are put on installation face 21 through vibration-proof leg parts 20a and 20b. In case that transmission part 6 and receiving part 7 are mounted, the handset of telephone set 5 is put through these leg parts 20a and 20b on the installation face normally. As a result, since the frame, the case stand related to the frame, and the case part can be omitted, the case can be small-size and light-weight, and the vibration-proof effect can be improved.