To sufficiently reduce the diameter of a light beam to be converged on each information recording layer by designing to minimize the spherical aberration of the light beam that converges on the information recording layer positioned nearest to the lens group, in compensating the spherical aberration of the light beam converging on each information recording layer by varying the interval of two lens groups.

The light passing through in the order of the first and the second element 4, 5 consisting of two lenses is constituted so that the light beam is converged without aberration on the information recording layer 6a or 6b of a recording medium 6. An objective lens is formed with two lenses by combining an objective lens with a semi-spherical lens, thereby relaxing the manufacturing and assembling tolerance of the lens, and enabling considerable number of apertures to be realized. In addition, in recording/reproducing on a multilayer recording medium, a light beam can be converged sufficiently small for each information recording layer by varying the interval of the two lenses. In other words, the quantity of spherical aberration can be increased/ decreased of the light beam emitted from the objective lens.