An overview of the present invention is described below. FIGS. 13(a) and 13(b) are block diagrams depicting an overview of a personal authentication device according to the present invention. The personal authentication device depicted in FIGS. 13(a) and 13(b) includes acoustic signal transmission means 701, acoustic signal observation means 702, acoustic property calculation means 703, and user identification means 704.

The acoustic signal transmission means 701 transmits a first acoustic signal to a part of the head of a user. For example, the acoustic signal transmission means 701 may be realized as an accessory or a device for producing an acoustic effect, which is attached to a region, or its vicinity, where a cavity or a bone is formed in the head of the user, in order to transmit the first acoustic signal.

The acoustic signal observation means 702 observes a second acoustic signal which is an acoustic signal after the first acoustic signal propagates through the part of the head. The part of the head as the propagation path of the acoustic signal may include at least a part of the skull, brain, sense organ, and cavity therebetween constituting the head.

The acoustic property calculation means 703 calculates an acoustic property from the first acoustic signal and the second acoustic signal.

The user identification means 704 identifies the user, based on the calculated acoustic property or a feature value extracted from the acoustic property and relating to the user.