A storage apparatus for which a hierarchical data management system is adopted is designed so that when receiving a read request for a first logical area to which a first storage area of a first storage device in a virtual volume is allocated, whether or not to migrate data in a first storage area of the first storage device, to a storage area of a second storage device is decided according to an access frequency to the first logical area in synchronization with the read request. When it is decided that the data stored in the first storage area of the first storage device should be migrated to the storage area of the second storage device, the data is migrated to a second storage area of the second storage device and the second storage area thereof is allocated to the first logical area in the virtual volume.