In order to reduce load at a resource managing node for exclusive control of a shared resource, each node has a group of lock state registers each corresponding to one of the nodes. Before one node issues a lock request to a resource managing node, the node checks the register group to see if the resource managing node is unlocked. With the target node found to be accessible, the access requesting node sends to a broadcast message exchange circuit a broadcast request message including a lock request regarding the resource managing node. The broadcast message exchange circuit receives such broadcast request messages from access requesting nodes, and changes them serially into broadcast messages for broadcast to all nodes. Of these broadcast messages, the first message received by each node is processed by its lock control circuit so that the lock request in that message is allowed to lock the resource managing node. The lock control circuit writes the number of the access requesting node into the register corresponding to the resource managing node. The access requesting node checks the register contents to see if the lock request it issued has been successfully accepted.