During registration, an iris image taken is frequency-analyzed using a plurality of frequencies f1 to fn to generate features for the respective frequencies f1 to fn. During authentication, frequencies f2 to fn are selected from the frequencies f1 to fn for use in frequency analysis for authentication. An iris image of a person to be authenticated taken is frequency-analyzed using the selected frequencies f2 to fn to generate features for the respective frequencies f2 to fn. The generated features are compared with the features generated for the same frequencies during the registration to perform personal authentication.