Provided is a personal authentication device or the like that can reduce the psychological and / or physical burden of a user to be authenticated and can easily ensure security. The personal authentication device 300 includes a sending unit 31 that sends a first acoustic signal to a part of the user's head, and a second acoustic signal after the first acoustic signal propagates through a part of the user's head. An observation unit 32 for observing the acoustic signal, a calculation unit 33 for calculating an acoustic characteristic from the first acoustic signal and the second acoustic signal, an extraction unit 34 for extracting a feature quantity related to the user from the acoustic characteristic, and a first feature quantity. Control unit 35 registered in the storage unit as the feature amount of the first, and the user is identified by collating the first feature amount registered in the storage unit and the second feature amount extracted after registration of the first feature amount And a storage unit 37 for storing the first feature value. When the identification unit 36 identifies the user as the same, the transmission unit 31 transmits the first acoustic signal at predetermined intervals.認証対象のユーザの心理的および／または肉体的な負担が少なく、簡単にセキュリティを担保できる個人認証装置等を提供する。個人認証装置３００は、ユーザの頭部の一部に第１の音響信号を送出する送出部３１、第１の音響信号がユーザの頭部の一部を伝播した後の音響信号である第２の音響信号を観測する観測部３２、第１の音響信号および第２の音響信号から音響特性を算出する算出部３３、音響特性からユーザに関する特徴量を抽出する抽出部３４、特徴量を第１の特徴量として記憶部に登録する記憶制御部３５、記憶部に登録される第１の特徴量と第１の特徴量の登録後に抽出される第２の特徴量とを照合してユーザを識別する識別部３６、第１の特徴量を記憶する記憶部３７を備え、識別部３６がユーザを同一と識別する場合所定間隔毎に送出部３１は第１の音響信号を送出する。
