Abstract: The storage virtualization apparatus is capable of identifying a host computer or computers within an extent of influence and restraining of the extent when a physical storage enclosure has a breakdown or stops. The storage virtualization apparatus of the present invention comprises: first connection means for connecting to a host computer; second connection means for communicating with a plurality of physical storage enclosures; virtualization means for making the host computer recognize a storage area constituted by parts or all of storage areas of the physical storage enclosures as a virtual storage enclosure or enclosures; and grouping means for dividing the physical storage enclosures into a plurality of groups so as to constitute each virtual storage enclosure with the storage areas of the physical storage enclosures in the same group.