1. A personal authentication method using biological information, the method using a biological feature database storing feature information of a plurality of types of biological features and information on the relationship between the combination of biological features used for authentication and authentication precision, for persons including at least a person to be authenticated, the method comprising the steps of: acquiring feature information of at least one type of biological feature among the plurality of types for the person to be authenticated; performing authentication using the acquired feature information and the feature information of the corresponding biological feature stored in the biological feature database; and determining authentication precision for the authentication based on a combination of biological features related to the acquired feature information by referring to the biological feature database.