A storage device includes storage units, a management section that manages a logically defined storage area as a real logical volume by associating the storage area with a physical storage area created using the storage units in advance and manages the logically defined storage area as a virtual logical volume by associating the storage area with a physical storage area when data is added, a determination section that determines whether the activity ratio of the virtual logical volume exceeds a threshold and whether the physical storage area associated with a storage area of the virtual logical volume is managed by another control unit, and a migration section that migrates data stored in the virtual logical volume to a real logical volume when the activity ratio exceeds the threshold and the physical storage area associated with the storage area of the virtual logical volume managed by another control unit.