An optical disk duplicating apparatus comprises reproducing means for reproducing user's data recorded on a first optical disk, adding means for adding sector data identification information indicative of the state of using sectors in recording tracks on the first optical disk to the reproduced user's data, recording means for recording the user's data on a second optical disk, and transfer means for transferring the user's data and the sector data identification information to the recording means. The optical disk duplicating apparatus determines whether each of the sectors in the first optical disk has data properly recorded therein, a defective sector identifier portion, a defective data field portion, or no signal recorded therein, by using the sector data identification information and controls a signal supplied to the recording means, thereby producing duplicated sectors in a manner such that the sectors in the first optical disk correspond respectively to the sectors in the second optical disk on the sector-to-sector basis.