A network system including a management device with both a status managing unit for collecting status information on a terminal status and a terminal instructing unit for transmitting a shift start message to the terminal to make transfer data to the server on the basis of the status information collected by the status managing unit. The terminal includes a determining unit for determining data transfer in response to the shift start message, a data transferring unit for transferring the data to the server when the determining unit determines the data transfer, a storage device control unit for erasing the data from a storage device after completion of data transfer, and a thin client shifting unit for causing the terminal to function as a thin client after erasure of data.