In a net boot type thin client system, bottle necks concentrate on specific steps in a previously downloading method and an on-demand downloading method so as to hinder high-speed operation. Specifically, a previously file acquiring section for acquiring a file before the OS operates, an on-demand file acquiring section for acquiring a file while the OS operates, and a file determining section for determining whether or not a file is used in a high frequency. A high use-frequency file is downloaded before an OS operates and a low use-frequency file is downloaded while the OS operates.