Patent ID: 7068588

Claim:
An optical disk medium having a disk shape and comprising: recorded information tracks formed in a concentric or spiral manner; and a transparent substrate or a transparent cover layer through which the recorded information tracks are irradiated by a laser beam to record or play back information; when the lens numerical aperture of an objective lens through which the laser beam irradiates the optical disk medium is denoted by NA, the wavelength of the laser beam is denoted by λ μm, the refractive index of the transparent substrate or the transparent cover layer is denoted by n, the thickness of the transparent substrate or the transparent cover layer is denoted by d μm, and the minimum pit length of pits formed on the recorded information tracks is denoted by Lp μm, the relationships d≧ 200/tan(sin −1 (NA/ n )) and Lp≦ 0.35·λ/NA being satisfied; a change in the tilt of the surface of the optical disk medium over one circuit of each of the information tracks being equal to or less than a first predetermined value; a change in the tilt over the entire surface of the optical disk medium being equal to or less than a second predetermined value; and the second predetermined value being larger than the first predetermined value, wherein the first predetermined value is equal to or less than 38·λ/(NA 3 ·d)·n 3 /(n 2 −1) deg.