When, in a network computer system, a Web browser on a host computer acquires information about images or the like from a network or the like, it analyzes the data received in a proxy server, and, in case the details of the data are moving images, transmits substitute images with the same screen size to host computer, and transmits the moving image access information toward user computer. In case substitute images have been transmitted by proxy server, host computer transmits, to user computer, the display position and screen size of the moving images and information indicating Web server saving the moving images. In this way, it is possible, even when a host computer is remotely operated from a user computer via a network and moving images are displayed, to play back the moving images smoothly.