A magnetic field corresponding to an acoustic signal is generated from an antenna, and by using a coil, it can be converted into an acoustic signal again. It is possible to estimate the location of the invisible antenna from the distribution of the received signal. This estimation is applied to the maintenance of gas pipes on the situation that the distance from the entrance to a maintenance area is known, but the piping route is unknown. It is possible to identify the maintenance areas of a gas pipe by inserting an antenna. The estimation is performed by manually listening to the received signal. However, it is difficult to identify an accurate point because there are only subtle differences between the volumes of each place. To solve this problem, we visualize the distribution of the received signal, and estimate the magnetic field using only acoustic signal. In addition, we propose a method to estimate the location of the invisible antenna automatically by using the symmetry of the distribution of the received signal.