An information processing system includes a first authentication terminal for authenticating a first user, a second authentication terminal for authenticating a second user, a device for authenticating the device, and an authentication server that performs authentication using a registered authentication function. The authentication server registers an authentication function of the first authentication terminal based on an operation of the first user. When authentication using the first authentication terminal is requested through the device, the authentication server authenticates the first user and registers an authentication function of the device. When registration of an authentication function of the second authentication terminal is requested through the device, the authentication server registers the authentication function when the authentication function of the device has been registered. When authentication using the second authentication terminal is requested, the authentication server authenticates the second user when the authentication function of the second authentication terminal has been registered.