PURPOSE: To make improvements in remote controllability by slinging an underwater acoustic relay station being electrically connected to a floating body with a wave transceiver function, and making it so as to correspond with an object, in case of correspondence with an unroped, unmanned diving machine or the like.

CONSTITUTION: A radio wave W transmitted out a mother ship 5 is received by an antenna 2 of a buoy 1 and, after being converted into an electric signal, it is transmitted to an underwater acoustic relay station 4 via a composite cable 3. Then, it is further converted into an ultrasonic wave M and transmitted to an unroped, unmanned diving machine 6 which receives this ultrasonic wave M and is controlled. On the other hand, the ultrasonic wave M being outputted out of this diving machine 6 is outputted from the antenna 2 of the buoy 1 as a wave signal and fed to the mother ship 5. With this constitution, remote controllability is well improvable.