Additional recording data is written continuously with data already recorded on a disk and writing of additional data is started in synch with recorded data. The optical head 1 reads data recorded on the disk just before recording is halted every time the record decision unit 22 judges that recording is to be halted. The record-status detection unit 25 detects the formation status of the recorded data. The head output control unit 14 sets the luminous output of the optical head 1 at the beginning of additional writing according to the recording state judged by the record-state detection unit 25. Thus, the formation status of data recorded on a disk is detected to allow the luminous output of the optical head 1 to be set to an optimum record level.