To provide a user authentication system capable of preventing an improper individual authentication.

This system comprises an information management part 12 for retaining personal information related to a registered user and question information for inquiring the personal information; a questioning control part 13 for selecting the question information; a questioning part 14 for supplying the question information to an applicant user; and a determination part 15 for determining the correctness for answer information based on the personal information, supplying the determination result to the questioning control part, and determining the propriety of authentication of the applicant user. The questioning control part 13 records the history of the determination result, and selects, when selecting question information, question information except the question information for which errors in answers are recorded in the history of a prescribed period from the present time to the past.