Input information acquisition means (101, 201) of an authentication system (S) acquires input information, which accompanies a card possessed by a user, and has been input from a user terminal through use of reading means (33A) or photographing means (36). Identification information acquisition means (102, 202) acquires identification information that enables identification of the card. Registered information acquisition means (105, 203) acquires registered information, which accompanies the card, and has been registered in a server in association with the identification information in advance. Authentication means (103) executes authentication based on the input information and the registered information.