Abstract: A masking member is provided so as to move in an interlocked manner with a shift of an objective lens designed for a high-density disk. Since the masking member reduces an effective numerical aperture (NA) of the objective lens, and greatly reduces affection of aberration, the objective lens allows a CD whose substrate is thicker than that of the high-density disk to be stably reproduced. Also, for example, even when the objective lens moves in a track direction of the high-density disk or CD, the masking member follows that movement. Therefore, a suitably sized light spot is formed on a signal surface of the high-density disk or CD. Especially, a light flux having passed inside the masking member with relatively small aberration is used to form a suitably sized light spot on the signal surface of the CD.

Abstract: In an optical recording and reproducing device, an aperture member is provided in a region between an objective lens and a reflection mirror so as to be freely pushed into and pulled out of a light flux, and a masking member is provided on the objective lens. The masking member has an inside diameter smaller than an aperture diameter of the aperture member, and has an outside diameter greater than the aperture diameter of the aperture member. The aperture member has an outline size greater than a size of an aperture of an objective lens holding member. Therefore, an effective numerical aperture of the objective lens is determined in accordance with the inside diameter of the masking member in the case where the aperture member is placed in the light flux, whereas the effective numerical aperture is determined by the aperture of the objective lens holding member in the case where the aperture member is not placed in the light flux.