An authentication system that executes user authentication processing in accordance with an authentication request, comprising: at least one first device that is configured to acquire biological information of a user, the first device having: a biological information acquiring unit that is configured to acquire the biological information of the user; and a first authentication unit that is configured to output an authentication result of user authentication, as an authentication for the user to use the first device, based on the biological information; and a second device that is configured to communicate with the first device, the second device having: an information acquiring-storing unit that is able to store identification information of the first device beforehand; a determination unit that is configured to determine whether the first device is registered, based on identification information received from the first device and the identification information in the information acquiring-storing unit; and a second authentication unit that is configured to perform user authentication, as an authentication for the user to use the second device, in accordance with the authentication result output by the first authentication unit that is received from the first device, when the determination unit determines that the first device is registered, wherein the first device is configured to, if the authentication result output by the first authentication unit indicates the authentication for the user to use the first device, transmit the identification information for identifying the first device to the second device, and wherein the second authentication unit is configured to, when the determination unit determines that the first device is not registered, further execute an additional authentication different from the authentication by the first authentication unit and authenticate the user in accordance with an authentication result of the additional authentication. at least one first device that is configured to acquire biological information of a user, the first device having: a biological information acquiring unit that is configured to acquire the biological information of the user; and a first authentication unit that is configured to output an authentication result of user authentication, as an authentication for the user to use the first device, based on the biological information; and a biological information acquiring unit that is configured to acquire the biological information of the user; and a first authentication unit that is configured to output an authentication result of user authentication, as an authentication for the user to use the first device, based on the biological information; and a second device that is configured to communicate with the first device, the second device having: an information acquiring-storing unit that is able to store identification information of the first device beforehand; a determination unit that is configured to determine whether the first device is registered, based on identification information received from the first device and the identification information in the information acquiring-storing unit; and a second authentication unit that is configured to perform user authentication, as an authentication for the user to use the second device, in accordance with the authentication result output by the first authentication unit that is received from the first device, when the determination unit determines that the first device is registered, wherein the first device is configured to, if the authentication result output by the first authentication unit indicates the authentication for the user to use the first device, transmit the identification information for identifying the first device to the second device, and wherein the second authentication unit is configured to, when the determination unit determines that the first device is not registered, further execute an additional authentication different from the authentication by the first authentication unit and authenticate the user in accordance with an authentication result of the additional authentication. an information acquiring-storing unit that is able to store identification information of the first device beforehand; a determination unit that is configured to determine whether the first device is registered, based on identification information received from the first device and the identification information in the information acquiring-storing unit; and a second authentication unit that is configured to perform user authentication, as an authentication for the user to use the second device, in accordance with the authentication result output by the first authentication unit that is received from the first device, when the determination unit determines that the first device is registered, wherein the first device is configured to, if the authentication result output by the first authentication unit indicates the authentication for the user to use the first device, transmit the identification information for identifying the first device to the second device, and wherein the second authentication unit is configured to, when the determination unit determines that the first device is not registered, further execute an additional authentication different from the authentication by the first authentication unit and authenticate the user in accordance with an authentication result of the additional authentication.