PURPOSE: To attain underwater transmission/reception simply and accurately by adopting communication under water through an ultrasonic wave transmission medium, receiving a coded signal corresponding to a message at a message destination station to apply signal processing and demodulating the signal as voice or significant character information according to the correspondence processing.

CONSTITUTION: A data signal corresponding to a message is sent from a ship installation 3, a prescribed signal is added to the data signal by a controller 3b and the resulting signal is sent to a repeater 8 as a radio signal. The repeater receives a radio wave signal and sends it to a controller 6b via an underwater ultrasonic wave transducer 8b. Then the reception of the data is informed to a diver 6 through vibration delivery such as skin stimulation or bone conduction in the incoming function of the controller 6b. Then the data signal is received as voice by a voice synthesizer or significant character information by a character converter corresponding to the message by means of a speaker or a display device.