PURPOSE: To provide a required acoustic signal without sending the acoustic signal to the unrequired space and without the physical restriction by emitting the soundwave corresponding to the audible modulation signal by taking the space corresponding to the focusing position of the rotating ellipsoid as a sound source.

CONSTITUTION: An originating ultrasonic transducer 3 is installed on the inside focus 2 of a part 1 of a rotating body. The ultrasonic output of the transducer 3 is emitted towards the part 1 of the rotating ellipsoid. Then, it is converted into another focus 8 and it is further converged and diverged. In passing the route, the ultrasonic wave takes the audible signal whose amplitude is modulated as the isolate sound source gradually and it is separated and generated. Thus, the audible soundwave is included in the direction shown by the doted lines. Thus, when a listner 9 is in the divergence area after the convergence, he hears the soundwave as the sound source of the sound wave is in the focus 8. In this case, the audible sound wave is not beyond the doted line range and the listner 9 does not hear the sound source other than the focus 8.