Here, the removal means may, using acoustic signals observed as a result of transmitting the acoustic signal to each of the right and left ear canals and/or pinnae, remove ambient noise and/or a device property from at least one of the observed acoustic signals.

(Supplementary note 6) The personal authentication device according to any one of supplementary notes 1 to 5, wherein the acoustic signal transmission means transmits an acoustic signal for bone conduction, as the first acoustic signal, and the acoustic signal observation means observes the second acoustic signal after the first acoustic signal propagates through the part of the head by bone conduction, as the second acoustic signal.

Here, the acoustic signal observation means may be realized by a bone conduction microphone. Moreover, the acoustic signal observation means may observe the second acoustic signal from a part different from the part of the head to which the acoustic signal transmission means transmits the first acoustic signal.

(Supplementary note 7) The personal authentication device according to any one of supplementary notes 1 to 6, including noise estimation means for estimating a noise signal, based on an acoustic signal observed by the acoustic signal observation means, wherein the acoustic signal transmission means transmits an acoustic signal of a frequency band different from a frequency band of the noise signal estimated by the noise estimation means, as the first acoustic signal from next time.

(Supplementary note 8) The personal authentication device according to any one of supplementary notes 1 to 7, wherein the acoustic signal transmission means changes the first acoustic signal regularly or irregularly.