Optical disk, optical disk apparatus, optical disk recording and reproduction method, and apparatus and method for recording BCA code

A disk (1) has a burst cutting area (BCA) (10) formed by a crystalline portion and an amorphous portion, and the disk (1) is an optical disk (L-H medium) in which the reflectance of the crystalline portion is lower than that of the amorphous portion. The width Wcry of the crystalline portion in the BCA (10) is lower than half the data period Wdat. Therefore, the average level of a BCA reproduction signal is unchanged regardless of whether the optical disk is an H-L medium or an L-H medium, so that focus control and reproduction of a BCA code can be performed even if a parameter of a circuit is a default.