Operation in this exemplary embodiment is described below.

FIG. 3 is a flowchart depicting an example of the operation of the personal authentication device in this exemplary embodiment. In the example depicted in FIG. 3, first the acoustic signal transmission means 101 transmits an acoustic signal to the part of the head of the user to be authenticated (step S101). The acoustic signal transmission means 101 may, for example, transmit the acoustic signal from the entrance of the ear canal into the ear canal. The acoustic signal may be a maximal length sequence (M-sequence) signal, a time stretched pulse (TSP) signal, or the like widely used for the purpose of measuring an impulse response.

FIG. 4(a) is a graph depicting an example of the acoustic signal transmitted by the acoustic signal transmission means 101. In the graph in FIG. 4(a), the horizontal axis represents time t, and the vertical axis represents the signal value x(t) of the acoustic signal transmitted at time t. The acoustic signal transmitted by the acoustic signal transmission means 101 is hereafter also referred to as “transmission acoustic signal”.

Subsequently, the acoustic signal observation means 102 observes an acoustic signal after the transmission acoustic signal propagates through the part of the head of the user to be authenticated (step S102).