A computing system and an exclusive access control method are provided for preventing degraded performance of a network caused by exclusive access control, and for permitting a computer to exclusively access a storage area irrespective of whether a storage has an exclusive access control function. In the computing system in which a plurality of computers and an external storage device storing shared data are connected through a relay, exclusive access control is executed by a device other than the storage. Specifically, the relay having a virtualizing function is instructed to execute exclusive access control. The relay has information indicating whether a storage area on the storage is an exclusive access area, so that the relay determines based on this information whether an access request received from a computer requests an access to an exclusive access area, and executes exclusive access control when it is an access request.