In order to improve the safety and reliability of services provided by a computer, an authentication device (1) equipped with a transmission unit (15) and a determination unit (16) is provided. The transmission unit (15) transmits a challenge to a terminal device (7) where the challenge is presented to a user (8) to be authenticated, the challenge being information serving as the basis on which the user inputs information to be used for authentication processing. At this time, the transmission unit (15) transmits a plurality of different challenges to the terminal device (7). The determination unit (16) determines not only whether or not a response input to the terminal device (7) by the user (8) in response to each challenge is correct, but also whether or not time information regarding the challenge and the response thereto satisfies a condition regarding the response.