To read out a different optical disk in thickness by using a light source for selectively generating a different wavelength.

At the time of reproducing an information signal on a recording surface of a thin film optical disk 252, light of a wavelength λ1 is generated by a light source 210. Only the light of the wavelength λ1 is transmitted to an objective lens 240 through a 1st part 232 in an annular disk shape of an optical device 230, and light of the other wavelengths is reflected. Tertiary component light of the light of the wavelength λ1 transmitted through the part, 232 is converged on the recording surface of the disk 252 via a peripheral part of a larger numerical aperture than a numerical aperture of the middle part of the lens 240. On the other hand, at the time of reproducing an information signal on a recording surface of a thick film disk 256, light of a wavelength λ2 is generated by the light source 210. Only the light of the wavelength λ2 is transmitted through a 2nd part 234 of the device 230, and light of the other wavelengths is reflected. The transmitted light is passed through the middle part of the lens 240 and converged on the recording surface of the disk 256. Thus, by providing the light source capable of selectively generating one of light beams of different wavelengths, recorded information on the thin or thick film disk can be readout.