A personal authentication device comprising: a storage means for storing first identification information for identifying a user, as registered first identification information, and second identification information, being different from the first identification information and for continuously identifying the user, as registered second identification information; an analysis means for analyzing information inputted from a user and generating first identification information, as generated first identification information; a transmission means for transmitting a first acoustic signal toward a cavity of a head of the user from an entrance of the cavity, the cavity being an ear canal; an observation means for observing a second acoustic signal that is an acoustic signal after the first acoustic signal propagates through the cavity of the head of the user; a calculation means for calculating acoustic characteristics from the first acoustic signal and the second acoustic signal; an extraction means for extracting an acoustic feature amount related to the user from the acoustic characteristics as second identification information; and the personal authentication device being characterised in that it further comprises: a storage control means configured, when an application is started, to store the extracted second identification information in the storage means, as the registered second identification information, wherein when the application is being executed, the transmission means, the observation means, the calculation means, and the extraction means are configured to repeat their respective operations, thereby extracting anew second identification information, a determination means for determining the user to be identical when the registered first identification information in the storage means and the generated first identification information coincide with each other as a collation result, and the registered second identification information in the storage means and the second identification information extracted anew coincide with each other as a collation result, and the storage control means is further configured to delete the registered second identification information from the storage means when the application is stopped. a storage means for storing first identification information for identifying a user, as registered first identification information, and second identification information, being different from the first identification information and for continuously identifying the user, as registered second identification information; an analysis means for analyzing information inputted from a user and generating first identification information, as generated first identification information; a transmission means for transmitting a first acoustic signal toward a cavity of a head of the user from an entrance of the cavity, the cavity being an ear canal; an observation means for observing a second acoustic signal that is an acoustic signal after the first acoustic signal propagates through the cavity of the head of the user; a calculation means for calculating acoustic characteristics from the first acoustic signal and the second acoustic signal; an extraction means for extracting an acoustic feature amount related to the user from the acoustic characteristics as second identification information; and the personal authentication device being characterised in that it further comprises: a storage control means configured, when an application is started, to store the extracted second identification information in the storage means, as the registered second identification information, wherein when the application is being executed, the transmission means, the observation means, the calculation means, and the extraction means are configured to repeat their respective operations, thereby extracting anew second identification information, a determination means for determining the user to be identical when the registered first identification information in the storage means and the generated first identification information coincide with each other as a collation result, and the registered second identification information in the storage means and the second identification information extracted anew coincide with each other as a collation result, and the storage control means is further configured to delete the registered second identification information from the storage means when the application is stopped. a storage control means configured, when an application is started, to store the extracted second identification information in the storage means, as the registered second identification information, wherein when the application is being executed, the transmission means, the observation means, the calculation means, and the extraction means are configured to repeat their respective operations, thereby extracting anew second identification information, a determination means for determining the user to be identical when the registered first identification information in the storage means and the generated first identification information coincide with each other as a collation result, and the registered second identification information in the storage means and the second identification information extracted anew coincide with each other as a collation result, and the storage control means is further configured to delete the registered second identification information from the storage means when the application is stopped.