All operations available on an intranet are securely performed from an outside of the intranet without taking out a file on the intranet from the intranet. A file on the intranet is not taken out, but, instead of this, image information on a target computer 1 is transmitted to an operational computer 4 with the http protocol, the https protocol, or the SSL protocol, and keyboard information, pointing information, or the like are transmitted from an operational computer 4 to the target computer 1. Consequently, the target computer 1 is operated.