A data management apparatus which includes: a removable storage device; a nonvolatile memory which saves a first conversion key; a first encrypting device which converts a datum to be saved in the storage device into an encrypted datum by the first conversion key; a first writing device which writes the encrypted datum into the storage device; a first reading device which reads the encrypted data; a first decrypting device having a second conversion key which decrypts the encrypted datum by the second conversion key; a second encrypting device having a third conversion key which encrypts the second conversion key by the third conversion key, and converts the second conversion key into a fourth conversion key; a second writing device which writes the fourth conversion key into the storage device; a second reading device which reads the fourth conversion key; and a second decrypting device which decrypts the fourth conversion key.