A user terminal device constituting part of a thin client system that transfers and stores confidential data to a file server, comprising: a secondary storage device; file access control means that determines the kind of an I/O request issued to the secondary storage device and determines, if the I/O request is a write request, if an application that is the source of the I/O request is permitted to write data to the secondary storage device; write control means that redirects and stores to a cache memory the confidential data which is not permitted to be written in the secondary storage device and control data which is permitted to be written in the secondary storage device, wherein the confidential data is data that has been requested to be written by an application that is not permitted to write data to the secondary storage and the control data is data that has been requested to be written by an application that is permitted to write data to the secondary storage device; upload data management means (107, 209) that, if the application that is the source of the I/O request is not permitted to write data to the secondary storage device, manages and uploads to the file server the confidential data that has been requested to be written; and automatic backup means that reads the confidential data managed by the upload data management means (107, 209) from the cache memory and uploads it to the file server at the time of shutting down the user terminal device, wherein: the write control means includes first redirecting means that processes a write request and a read request, and second redirecting means that processes only a write request, the first redirecting means, if the file access control means has determined that the application that is source of the write request is not permitted to write data to the secondary storage device, stores the confidential data into the cache memory, each of the first redirecting means and the second redirecting means (212, 213), if the file access control means has determined that the application that is the source of the write request is permitted to write data to the secondary storage device, stores into different two locations in the cache memory the control data that has been requested to be written, and, the second redirecting means writes the control data stored in the cache memory to the secondary storage device at the time of shutting down the user terminal device. a secondary storage device; file access control means that determines the kind of an I/O request issued to the secondary storage device and determines, if the I/O request is a write request, if an application that is the source of the I/O request is permitted to write data to the secondary storage device; write control means that redirects and stores to a cache memory the confidential data which is not permitted to be written in the secondary storage device and control data which is permitted to be written in the secondary storage device, wherein the confidential data is data that has been requested to be written by an application that is not permitted to write data to the secondary storage and the control data is data that has been requested to be written by an application that is permitted to write data to the secondary storage device; upload data management means (107, 209) that, if the application that is the source of the I/O request is not permitted to write data to the secondary storage device, manages and uploads to the file server the confidential data that has been requested to be written; and automatic backup means that reads the confidential data managed by the upload data management means (107, 209) from the cache memory and uploads it to the file server at the time of shutting down the user terminal device, wherein: the write control means includes first redirecting means that processes a write request and a read request, and second redirecting means that processes only a write request, the first redirecting means, if the file access control means has determined that the application that is source of the write request is not permitted to write data to the secondary storage device, stores the confidential data into the cache memory, each of the first redirecting means and the second redirecting means (212, 213), if the file access control means has determined that the application that is the source of the write request is permitted to write data to the secondary storage device, stores into different two locations in the cache memory the control data that has been requested to be written, and, the second redirecting means writes the control data stored in the cache memory to the secondary storage device at the time of shutting down the user terminal device. the write control means includes first redirecting means that processes a write request and a read request, and second redirecting means that processes only a write request, the first redirecting means, if the file access control means has determined that the application that is source of the write request is not permitted to write data to the secondary storage device, stores the confidential data into the cache memory, each of the first redirecting means and the second redirecting means (212, 213), if the file access control means has determined that the application that is the source of the write request is permitted to write data to the secondary storage device, stores into different two locations in the cache memory the control data that has been requested to be written, and, the second redirecting means writes the control data stored in the cache memory to the secondary storage device at the time of shutting down the user terminal device.