Abstract: A storage switch includes: a section 2 that creates a destination virtual disk having a capacity larger than that of a source virtual disk; a section 3 that creates a first area in the destination storage area, creates a mirror area for performing control so that processing corresponding to a write request to the source virtual disk is executed between the first area and source virtual disk, creates a second area in the destination virtual disk, creates a mirror area for performing control so that processing corresponding to a request to the second area is executed in the second area, and combines the created mirror areas to create a combined mirror area; a section 4 that connects the combined mirror area to a virtual target; and a section 5 that performs data migration from the source virtual disk to the first area.