A relay server and a relay communication system can easily synchronize resource information with a resource when terminals share the resource. When an instruction to synchronize shared resource information is given, the relay server transmits the synchronization instruction to each resource sharing terminal based on the shared resource information. Having received the synchronization instruction, when the shared resource information includes the resource that is owned by the terminal, the resource sharing terminal compares the resource information and the resource. If the resource information and the resource do not match, the resource sharing terminal updates the resource information to the latest information, and transmits, to the relay server, an instruction to update the shared resource information including the resource information. Thus, the resource information of an entire network can be synchronized by one synchronization instruction.