PURPOSE: To smoothly execute a communication among more than three persons by transmitting a transmitting person code, which is previously set, with a voice code and expressing the transmitting person in a voice on a reception side.

CONSTITUTION: By operating a switch, the transmission of a command is executed and at this time a transmitting person code switch 2 previously set besides an input switch 1 is provided so as to read the transmitting person code 2 at the time of entry of a power source or at the time of operating the input switch and input it in an encoder 3 with code data from the input switch. The encoder 3 codes the code data and the transmitting person code in a specified format. Next the signal is modulated, for instance in terms of AM modulation, in a modulation circuit 4 and amplified in a power amplifier 5 in order that an ultrasonic signal is radiated into the water from an ultrasonic transducer 7 through a circulator 6. In the voice synthesizing output circuit 12 of the reception part, the voice data corresponding to the voice code data and the transmitting person code is read out from a ROM where they are previously recorded and D/A converted so as to be transmitted as an analog sound output.