A thin client-server system, in which a server having a database to store user data, and a thin client terminal (1, 1', 101) acquiring the user data from the server are connected each other through a network, wherein the thin client terminal (1, 1', 101) comprises: communication processing means for transmitting and receiving the user data; storage means for issuing a user data acquisition request to the server through the communication processing means, and for storing the user data, which is acquired from the server, in a volatile memory; and control means for judging whether or not a predetermined time has passed since completion of reference to the user data which is stored in the volatile memory, and for deleting the user data, which is stored in the volatile memory, in the case that the predetermined time has passed, characterized in that: the thin client terminal (1, 1', 101) further includes thin client terminal side authentication means for executing authentication to judge whether reference to the user data stored in the volatile memory is permitted or not, and the control means for controlling the thin client terminal side authentication means to execute the authentication in the case that the thin client terminal (1, 1', 101) exists outside of a service area in which the thin client terminal (1, 1', 101) can not be connected with the server, then permitting the reference to the user data, which is stored in the volatile memory, in the case that the authentication results in success and the predetermined time has not passed, and deleting the user data, which is stored in the volatile memory, in the case the authentication results in failure. communication processing means for transmitting and receiving the user data; storage means for issuing a user data acquisition request to the server through the communication processing means, and for storing the user data, which is acquired from the server, in a volatile memory; and control means for judging whether or not a predetermined time has passed since completion of reference to the user data which is stored in the volatile memory, and for deleting the user data, which is stored in the volatile memory, in the case that the predetermined time has passed, characterized in that: the thin client terminal (1, 1', 101) further includes thin client terminal side authentication means for executing authentication to judge whether reference to the user data stored in the volatile memory is permitted or not, and the control means for controlling the thin client terminal side authentication means to execute the authentication in the case that the thin client terminal (1, 1', 101) exists outside of a service area in which the thin client terminal (1, 1', 101) can not be connected with the server, then permitting the reference to the user data, which is stored in the volatile memory, in the case that the authentication results in success and the predetermined time has not passed, and deleting the user data, which is stored in the volatile memory, in the case the authentication results in failure. the thin client terminal (1, 1', 101) further includes thin client terminal side authentication means for executing authentication to judge whether reference to the user data stored in the volatile memory is permitted or not, and the control means for controlling the thin client terminal side authentication means to execute the authentication in the case that the thin client terminal (1, 1', 101) exists outside of a service area in which the thin client terminal (1, 1', 101) can not be connected with the server, then permitting the reference to the user data, which is stored in the volatile memory, in the case that the authentication results in success and the predetermined time has not passed, and deleting the user data, which is stored in the volatile memory, in the case the authentication results in failure.