Provided is a thin client system that automatically allows two types of user terminals, a network-boot-type user terminal and a screen-transfer-type user terminal, to share the same execution environment. A screen-transfer/network-boot switching system serves as a server function switching device used in the thin client system, including a server function switching section and a terminal process proxy execution section. The server function switching section accepts a connection request from the user terminal, and determines attribute of the user terminal. If the user terminal is the network-boot-type user terminal, the boot image transfer section transfers a boot image to the user terminal. If the user terminal is the screen-transfer-type user terminal, the boot image transfer section transmits a boot image to the terminal process proxy execution section. Moreover, the terminal process proxy execution section transmits screen information to the user terminal.