There are some cases that an accuracy is low for reading unique information identifying an individual from an optical disk which comprises a plurality of information layers.The optical disk according to the present invention is an optical disk which comprises a first information layer and a second information layer for holding information so that, by incident light, (1) the information will be reproduced or (2) the information will be recorded and reproduced. The optical disk comprises a BCA area which is formed in the first information layer and in which individual identification information uniquely given to the optical disk is recorded.