Within an optical disk apparatus for recording or reproducing information onto/from an optical disk 1, by irradiating one three (3) laser beams upon information recording surface RS thereof, each having wavelength different from each other, selectively, through a 3-wavelengths compatible objective lens 31, according to a method for discriminating a kind of optical disk loaded therein, focus sweep is conducted upon the optical disk loaded, in a descending order of distance between the position of the objective lens when it focus the laser beam upon the information recording surface and the disk surface DS, so as to detect a time between the disk surface DS and the information recording surface RS on the optical disk, from a reflection light obtained, and thereby discriminating the kind of the optical disk upon basis of the time between the reflections detected in the above.