To provide an objective lens capable of performing normal bright field observation, and further capable of performing differential interference observation etc., under transmission illumination and vertical illumination, suitable for a post-positioned optical system, and also, suitable for macro-observation, even in the objective lens of low magnification (magnification of ≤10 times) requiring a wide visible field.

The objective lens includes, in order from an object side, a first lens group G1 having positive refractive power as a whole, a second lens group G2 having negative refractive power as a whole, and a third lens group G3 having positive refractive power as a whole. The first lens group G1 includes a meniscus single lens having positive refractive power, whose convex surface faces the object side or a meniscus cemented lens having positive refractive power, whose convex surface faces the object side, and the second lens group G2 includes at least one cemented lens, and is nearly telecentric on the object side.