A client server system S includes a plurality of client terminal devices 3 capable to connect with display device 4, whose screen resolution is HD or SD, and a server device which provides image information to the plurality of client terminal devices s through wireless network N. The server device 1 is structured to include a sendable resolution determining program 1134 to make CPU 111 determine whether to convert HD image information into SD image information or not, and an image information sending program 1135 to make the CPU 111 send SD image information attached with SD information to the plurality of client terminal devices 3.