Exemplary embodiments of the present invention are described below, with reference to drawings. FIG. 1 is a block diagram depicting an example of the structure of a personal authentication device in Exemplary Embodiment 1. The personal authentication device depicted in FIG. 1 includes acoustic signal transmission means 101, acoustic signal observation means 102, acoustic property calculation means 103, feature extraction means 104, user identification means 105, and feature value storage means 106.

The acoustic signal transmission means 101 transmits an acoustic signal to a part of the head of a first user. The part of the head to which the acoustic signal is transmitted is a region where a cavity is formed in the head, and may be at least a part of a region to which an accessory or a device for producing an acoustic effect can be attached or brought close.

The acoustic signal observation means 102 observes an acoustic signal after the acoustic signal transmitted from the acoustic signal transmission means 101 propagates through the part of the head of the first user. More specifically, the part of the head which is the propagation path of the acoustic signal may be at least a part of the skull, brain, sense organ, and cavity therebetween constituting the head.

The acoustic property calculation means 103 calculates the acoustic property of the acoustic signal propagating through the part of the head of the user, based on the acoustic signal transmitted from the acoustic signal transmission means 101 and the acoustic signal observed by the acoustic signal observation means 102.