An authentication system is provided with a room-security device, and an information processing apparatus installed in a controlled area controlled by the room-security device, in which the room-security device and the information processing apparatus are connected in a network. The room-security device obtains, from a user, identification information, and transmits the identification information to the information processing apparatus, if the user is permitted to enter a room based on the obtained identification information. The information processing apparatus receives the identification information. If it is detected that the user is alone in the controlled area based on the received identification information, the information processing apparatus performs authentication based on the received identification information instead of asking the user to enter authentication information to obtain the authentication information.