A conventional data shared system using a plurality of processing nodes and data storage units in a storage area network using SAN OS was a volume-level locking or a file-system-level locking through one limited server. A locking system for SAN proposed this time is one that is a file-system-level locking and creates no single point of failure. Namely, the locking system is incorporated into each storage unit of Storage Area Network to run software. As a result, the storage unit is converted to an intelligent form and an acceptor (1) for a first protocol and an acceptor (2) for a second protocol coexist. This allows the acceptor (1) to perform a locking mechanism and the acceptor (2) to perform data transfer, so that the locking system that is a file system level locking and that creates no single point of failure can be realized. The plurality of protocols is thus used so as to execute data control and data transfer efficiently.