An authentication system includes node devices, wherein a first node device transmits the authentication information thereof to a second node device, the second node device selects third node devices that are requested to verify the validity of the received authentication information, and transmits the authentication information to each of the selected third node devices, the third node device records verification information that is used to verify the validity of the authentication information of the first node device, verifies the validity of the authentication information on the basis of the authentication information and verification information, and transmits the result information to the second node device, and the second node device further derives weighted values indicating the reliability of the each verification of the third node devices and authenticates the first node device on the basis of the each result information and the each weighted value received from the third node devices.