(Supplementary note 9) The personal authentication device according to any one of supplementary notes 1 to 8, wherein the first acoustic signal is musical sound.

(Supplementary note 10) The personal authentication device according supplementary note 9, wherein the acoustic signal transmission means transmits, as the first acoustic signal: an acoustic signal obtained by superimposing, on an acoustic signal of music, another acoustic signal for the purpose of improving the amplitude of a low-amplitude component in the musical sound; or an acoustic signal obtained by superimposing, on an acoustic signal of music, another acoustic signal for the purpose of compensating for a low-power component of the frequency components in the musical sound.

(Supplementary note 11) A personal authentication method including: transmitting a first acoustic signal to a part of a head of a user; observing a second acoustic signal which is an acoustic signal after the first acoustic signal propagates through the part of the head; calculating an acoustic property from the first acoustic signal and the second acoustic signal; and identifying the user, based on the acoustic property or a feature value extracted from the acoustic property and relating to the user.

(Supplementary note 12) The personal authentication method according to supplementary note 11, wherein the user is identified by comparing the acoustic property or feature value acquired from the second acoustic signal with an acoustic property or feature value stored in storage means for storing beforehand, for at least one person, an acoustic property at the time of propagation of an acoustic signal through a predetermined part of the head or a feature value extracted from the acoustic property.