OPTICAL DISK DEVICE

PROBLEM TO BE SOLVED: To enable the continuation of the recording or reproducing operation without interruption when the defective block is generated during the continuous recording or reproducing operation. SOLUTION: When the defective block is generated on the optical disk 71 during the data recording or reproducing operation, alternate data of the defective block or the address of the defective block are continuously stored in a defect list 3 during at least one of continued data is recorded or reproduced. Then, the arrangement is made so that the alternate data stored in an alternate buffer memory 2 are written into the spare area of the optical disk 71 and the address of the defective block stored in the defective list 3 is written into the defective control area of the optical disk 71, after the recording of at least one of the continued data is finished or the reproduction of it is finished, or when the optical disk is taken out.