PURPOSE: To compensate various aberrations excellently, increase working distance, and attain size reduction by using lens elements which have refractive indexes, focal lengths, etc., on specific conditions and constituting an objective lens for optical disks which consists of three positive, negative, and positive elements in three groups.

CONSTITUTION: The objective lens consists of the positive meniscus lens G1 having a convex surface on a light source side, the negative meniscus lens G2 having a convex surface on an optical disk side, and the positive meniscus lens G3 having a convex surface on the light source side successively from the light source side. Then, inequalities (1)W(4) hold, where (f) is the focal length of the whole lens system, r1, r3, and r5 are the radii of curvature of the 1st, the 2nd, and the 3rd lenses on the light source side, and n1 and n3 are the refractive indexes of the 1st and the 3rd lenses. Consequently, the working distance is ≥0.45 times the focal length, and the weight including the lens barrel is ≤0.4g when the focal length of the lens system is 4.5mm.