Systems and methods for easily and at high speed re-encrypting data recorded on a magnetic recording medium when the data is encrypted using an encryption key and the encryption key is changed. A track where effective user data is not recorded is set as a first reserved track, then data is read out from the first updating source track and decrypted using a first encryption key KEY 1, which is reencrypted using a second encryption key KEY 2 and recorded in the first reserved track, next, the first updating source track is set as a second reserved track, and a second updating source track is set, and the encryption key is updated by repeating these steps until all tracks to be subjected to the key updating processing have been subjected to the key updating processing.