To provide an authentication device preventing safety from being reduced when the upper limit of authentication retries while suppressing malicious use by physical analysis.

The authentication device includes: an input section 101 used for inputting authentication information; a determining section 102 determining whether a value calculated by inputting state information for specifying the number of authentication failures, to a first function coincides with a predetermined comparison value and whether the number of failures is smaller than a predetermined threshold; an authenticating section 104 carrying out authentication based on authentication information when the calculated value coincides with the comparison value and the number of failures is smaller than the threshold; and an updating section 105 updating state information of a state storage section 120 into '1' which specifies the number of failures, using update information stored in a parameter storage section 130 when authentication is unsuccessful, and updates the state information of the state storage section 120 into '0' which specifies the number of failures when the authentication is successful.