At the time of migrating encrypted data into another storage apparatus, decrypt this data after migration is simplified, and security against tapping, falsification and the like is maintained when a calculation method of encrypted data is re-written into another calculation method, and also access performance is improved. In a storage system 100 which is provided with a storage apparatus having a volume 120 and which is accessible from a host computer, it is made possible to execute the data migration when a storage apparatus provided with a mechanism capable of decrypting the encrypted data is chosen as a migration destination of this data, and also to keep holding surely the encrypted data by updating and saving again an encryption method applied to a encryption of the encrypted data into another method by internal processing of the apparatus even when the apparatus and the encryption method become obsolete.