The bone conduction signal transmission means 301 transmits a bone conduction signal which is an acoustic signal for bone conduction, from a part of the head as a transmission acoustic signal. The part of the head to which the bone conduction signal is transmitted is, for example, a region where a bone 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 bone conduction signal observation means 302 observes a bone conduction signal after the bone conduction signal transmitted from the bone conduction signal transmission means 301 propagates through the part of the head of the user, as an observation acoustic signal. The part of the head which is the propagation path of the bone conduction signal may be at least a part of the skull, teeth, brain, sense organ, and cavity therebetween constituting the head. The propagation path includes at least a bone.

The bone conduction signal observation means 302 may be realized by, for example, a bone conduction microphone. Here, the bone conduction signal observation means 302 may observe the bone conduction signal from a part different from the given part of the head to which the bone conduction signal transmission means 301 transmits the bone conduction signal. Exemplary Embodiment 3 is the same as Exemplary Embodiment 1 in other respects.

As described above, according to this exemplary embodiment, personal authentication can be performed by use of acoustic signal transmission property by bone conduction. This enables personal authentication to be performed without covering the user's auditory organ such as the ear.