An authentication system in which a first apparatus and a second apparatus are connectable via a network, comprising;: a first storage unit at the first apparatus configured to store first identification data and second identification data corresponding to the first identification data; a first transmitting unit at the second apparatus configured to transmit the third identification data; a first receiving unit at the first apparatus configured to receive third identification data; a first extracting unit at the first apparatus configured to determine whether first identification data are stored in the storage unit based on the third identification data; a second extracting unit at the first apparatus configured to extract second identification data corresponding to the first identification data determined to be stored in the storage unit by the first extracting unit; an authentication process unit at the first apparatus configured to execute authentication of a user based on the second identification data extracted by the second extracting unit, wherein the second identification data is user identification data; a second storage unit at the second apparatus configured to store user identification data and password, characterized in that the authentication system further comprises: a generation unit at the second apparatus configured to generate password based on user identification data obtained from the first apparatus in case where the authentication is success; and a determining unit at the second apparatus configured to determine whether the obtained user identification data and the password generated based on the obtained user identification data match the user identification data and the password stored in the second storage unit. a first storage unit at the first apparatus configured to store first identification data and second identification data corresponding to the first identification data; a first transmitting unit at the second apparatus configured to transmit the third identification data; a first receiving unit at the first apparatus configured to receive third identification data; a first extracting unit at the first apparatus configured to determine whether first identification data are stored in the storage unit based on the third identification data; a second extracting unit at the first apparatus configured to extract second identification data corresponding to the first identification data determined to be stored in the storage unit by the first extracting unit; an authentication process unit at the first apparatus configured to execute authentication of a user based on the second identification data extracted by the second extracting unit, wherein the second identification data is user identification data; a second storage unit at the second apparatus configured to store user identification data and password, characterized in that the authentication system further comprises: a generation unit at the second apparatus configured to generate password based on user identification data obtained from the first apparatus in case where the authentication is success; and a determining unit at the second apparatus configured to determine whether the obtained user identification data and the password generated based on the obtained user identification data match the user identification data and the password stored in the second storage unit. a generation unit at the second apparatus configured to generate password based on user identification data obtained from the first apparatus in case where the authentication is success; and a determining unit at the second apparatus configured to determine whether the obtained user identification data and the password generated based on the obtained user identification data match the user identification data and the password stored in the second storage unit.