PURPOSE: To obtain an objective lens for optical disk characterized by a long working distance, a wide picture angle and superior performance by satisfying a four-group and four-constitution lens system consisting of a negative meniscus lens, two biconvex positive lenses and a positive meniscus lens with prescribed conditions.

CONSTITUTION: The four-group and four-constitution lens system is constituted of the 1st lens which is a negative meniscus lens turns its projected surface to the optical disc 5 side, the 2nd and 3rd lenses which are biconvex positive lenses 2, 3 and the 4th lens which is a positive meniscus lens turns its recessed surface to the optical disk 5 side and satisfied with the following three conditions: 2.5<L/f <2.8; 0.75<r1/f<1.05 and r1<0; r2<r1+d1. Provided that L is the whole length of the lens system, (f) is the focal distance of the lens system, r1 and r2 are radiuses of curvature on the light source side and the disk side of the 1st lens respectively, and d1 is the thickness of the 1st lens. Consequently, the objective lens for optical disk characterized by a ling working distance, a wide picture angle and superior performance is obtained.