As described above, according to this exemplary embodiment, various noise such as ambient environmental noise, cardiac sound, respiratory sound, utterance, joint sound, and vibration and device property which is an individual device difference can be removed from the observation acoustic signal or its acoustic property or feature value. This enables more accurate personal authentication than in Exemplary Embodiment 1.

Exemplary Embodiment 3 of the present invention is described below. FIG. 9 is a block diagram depicting an example of the structure of a personal authentication device in Exemplary Embodiment 3 of the present invention. The personal authentication device depicted in FIG. 9 has a structure in which the acoustic signal transmission means 101 and the acoustic signal observation means 102 in the structure of Exemplary Embodiment 1 depicted in FIG. 1 are replaced with bone conduction signal transmission means 301 and bone conduction signal observation means 302.

Sound typically propagates through air as a main medium, but can also propagate through bones as a medium. The propagation of sound through bones as a medium is called bone conduction. Bone conduction propagation property has individuality, too. Hence, an observation acoustic signal obtained as a result of bone conduction can be used for personal authentication.