[0134] Here, k is a natural number fulfilling 1???k???n (n???3, n is a natural number). [0135] In order to locate the first defect management information area 709 and the second defect management information area 710 so as to substantially face each other regardless of which of the first to n'th recording densities is used, the number of blocks N which fulfills the relationships of 150????????1, ?