The acoustic signal transmission method is based on generating a synthesized sound electrical signal by electrically synthesizing an audible sound signal and another signal different than the audible sound signal at the sending side, and transmitting the synthesized sound electrical signal, and extracting the another signal different than the audible sound signal from the synthesized sound electrical signal at the receiving side. Here, generation of the synthesized sound electrical signal is made by using a data hiding technique, for example. Accordingly, the acoustic signal represented by the synthesized sound electrical signal can be heard by human ears in the same way as the audible sound signal, and the synthesized another signal cannot be detected by human ears. Here, the synthesized sound electrical signal can be transmitted as a sound wave in air space, as electrical signal through a transmission line or as radio signals such as infrared and electromagnetic waves.