Since only one golden image (GI) of a snapshot can exist and is shared among a plurality of storage apparatuses, there was a problem that migration or copy thereof deteriorates the capacity efficiency and increases the cost for managing consistency. The present invention solves the above-mentioned problem by either (1) a direct sharing method of generating a parent-child relationship of snapshots among different storage apparatuses at the time of creating differential LUs from the GI or (2) a virtual sharing method of creating virtual LUs of the GI in the respective storage apparatuses and creating differential LUs of the snapshots from the created virtual LUs, using a storage virtualization function among a plurality of storage apparatuses.