A KVM switch is connected to a server, and a client via a network. The KVM switch includes: a signal processing portion that receives an analog image signal corresponding to screen data displayed on a display device of the client from the server, executes analog/digital conversion to the analog image signal, and stores a converted digital image signal as the screen data into a memory; a detecting portion that, when new screen data is stored, detects data corresponding to a changing part of the new screen data to screen data that has already been stored into the memory; a thinning-out portion that thins out the detected data corresponding to the changing part; and a transmitting and receiving portion that transmits data corresponding to the changing part after the thinning-out to the client, and receives operation data from an input device connected to the client.