As described above, according to this exemplary embodiment, personal authentication is performed based on the characteristics that the acoustic property of an acoustic signal propagating through a part of the head of the user differs between persons. The acoustic property of the propagation through the part of the head of the user is a feature inside the living body unlike a feature observable from outside such as a face or a fingerprint, and therefore has low risk of leakage and is difficult to steal. Moreover, to obtain the acoustic property, two signals, i.e. the transmission acoustic signal and the observation acoustic signal, are necessary. This reduces the risk of acquisition through eavesdropping or the like and forgery, as compared with a method that uses one signal. Furthermore, the only action performed by the user to be authenticated for authentication in this exemplary embodiment is wearing a headphone or an earphone in which a microphone is embedded, or holding a mobile phone or the like with a microphone embedded in its receiver portion over the ear. Thus, according to this exemplary embodiment, the psychological/physical burden of the user can be lessened. For example, by using the personal authentication method in this exemplary embodiment in combination with a voice-based information distribution device such as music distribution, transceiver, and phone call, such personal authentication that puts no additional physical/psychological burden on the user from the original use state can be provided.