OPTICAL DISK DISCRIMINATING METHOD, OPTICAL DISK DISCRIMINATION CONTROL DEVICE, OPTICAL DISK DEVICE, INFORMATION SURFACE DISCRIMINATING METHOD, AND INFORMATION SURFACE DISCRIMINATION CONTROL DEVICE

PROBLEM TO BE SOLVED: To provide an optical disk device in which collision of a focusing means and an optical disk is reduced. SOLUTION: This optical disk device is an optical disk device which accesses at least two kinds of optical disks corresponding to the numerical apertures being different respectively. The device is provided with a numerical aperture changeable focusing part 302 for focusing a light beam on the information surface of the optical disk, a detecting part 112 for detecting reflected light from the optical disk 102 which is irradiated with the light beam by the focusing part 302, a setting control part 303 for setting the numerical aperture of the focusing part 302 to the smallest numerical aperture out of the different numerical apertures, and an optical disk discrimination control part 304 for discriminating the kind of a loaded optical disk 102 on the basis of a signal in accordance with the detected result of the reflected light from the optical disk 102 irradiated with the light beam in the first number of openings set by the setting control part 306. COPYRIGHT: (C)2005,JPO&NCIPI