An imaging lens includes a first lens group and a second lens group, arranged in this order from an object side to an image plane side. The first lens group includes a first lens, a second lens, and a third lens. The second lens group includes a fourth lens, a fifth lens, and a sixth lens. The second lens has a convex surface facing the image plane side near an optical axis thereof. The fifth lens has a concave surface facing the image plane side near an optical axis thereof. The sixth lens has a concave surface facing the object side near an optical axis thereof. The fifth lens has refractive power weaker than those of the fourth lens and the sixth lens. The second lens has a specific Abbe's number.