Abstract: Provided is a more secure thin client server system by suppressing increase of the number of sessions established between a thin client and a server when the server controls a USB device connected to a USB bus of the thin client. When a thin client OS detects that a USB device (D) which is one of a plurality of predetermined USB devices is connected, a USB general-purpose device driver that supports all of the plurality of predetermined USB devices is loaded, and a type of the USB device (D) is notified from the thin client to the server via a session used when the screen information or the like is transmitted between the thin client and the server. The server loads a device driver of the USB device (D), assuming that the USB device (D) is connected to a USB virtual bus driver working as a virtual USB bus.