When a replacement region administration method that uses NAPs of replacement regions upon multisession media is applied to a replacement region administration method of replacement regions upon rewritable media, in order to alleviate interruptions in recording due to excessive retries in the replacement process, as well as unnecessary conversion processing within a record/play device, the NAPs are updated in the process of initializing the media or the process of replacement thereupon such that defective blocks within the replacement region that are logged as Unusable Cluster or Usable Cluster Type 2 entries on the DFL are not denoted.