The storage system according to the present invention has a function to encrypt write data from the host and store the same in a storage media. Further, validation information of write data is added to the write data during storage thereof, and the data having the validation information added thereto is encrypted and stored in the storage media. When starting the storage system or restoring the encryption key information, the encrypted data stored in the storage media is read from the disk and decrypted prior to receiving a data access request from the host, and validation of data is performed using the validation information added to the decrypted data, so as to determine whether the encryption key stored in a storage controller is valid or not.