The overall processing performance of a storage apparatus is improved by migrating MPPK ownership with suitable timing.The storage apparatus comprises a plurality of microprocessors; a plurality of storage areas formed in a drive group configured from a plurality of physical drives; and a management unit which manages, as the microprocessors which possess ownership to the storage areas, the microprocessors which handle data I/Os to/from one or more storage areas among the plurality of storage areas, wherein the management unit detects variations in the processing loads of the plurality of microprocessors, generates, on the basis of variations in the processing load, load balancing target information which includes information on the storage areas to which the ownership is migrated, information on the migration-source microprocessor serving as the migration source of the ownership, and information on the migration-destination microprocessor serving as the migration destination of the ownership, and migrates the ownership to the storage areas with timing such that there is no drop in the processing load of the migration-destination microprocessor contained in the load balancing target information.