The feature extraction means 104 calculates a feature value relating to the user in which the acoustic signal has propagated, from the calculated acoustic property.

The feature value storage means 106 stores an extracted feature value for at least one predetermined user beforehand. Each user for which a feature value is stored in the feature value storage means 106 is hereafter also referred to as “registered user”. For example, the feature value storage means 106 may store beforehand, for each of a plurality of users, a feature value extracted using a feature value extraction process by the acoustic signal transmission means 101, the acoustic signal observation means 102, the acoustic property calculation means 103, and the feature extraction means 104 or their equivalent structure.

The user identification means 105 compares the feature value obtained by the feature extraction means 104 with the feature value of the registered user stored in the feature value storage means 106, to determine whether or not the first user corresponds to the registered user.

FIG. 2 is a schematic diagram depicting an example of the specific structure of the personal authentication device in this exemplary embodiment. The personal authentication device depicted in FIG. 2 includes a personal computer (PC) 11, a sound processor 12, a microphone amplifier 13, an earphone 14, and a microphone 15. Reference sign 16 is the user (subject) to be authenticated.