A relay server is capable of communicating with other relay servers through an external server arranged on a Wide Area Network. The relay server stores information about a registered terminal, information about the relay servers forming a relay group by permitting connection among each other, and information about a resource and a client terminal sharing the resource. When an operation instruction regarding the resource in another terminal is received, the relay server relays the operation instruction from the registered terminal to another relay server. However, when key information is stored in association with the resource, the relay server relays the operation instruction to the other relay server only when a correct key has been entered.