When a computer system including a data storage apparatus having a data storage area storing encrypted data is modified to have plural encryption/decryption units, a computer cannot appropriately use the encrypted data storage area if a path including the encryption/decryption means is not adequately determined.In a computer system having a computer 10, two or more data storage apparatuses 100 and 200 arranged hierarchically, plural encryption/decryption modules 199 and 299 on a path between the computer 10 and a data storage area 101, and a management computer 500 for managing the data storage apparatuses and the like, if there is an interoperability between the encryption/decryption modules 199 and 299 and the data storage area 101 is encrypted by the first encryption/decryption module 199, the computer 10 accesses the data storage area 101 using the second encryption/decryption module 299 (or an n-th encryption/decryption module closer to the computer than the second encryption/decryption module), rather than the first encryption/decryption module.