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 having negative refractive power, and a sixth lens having positive refractive power. The first lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii. The sixth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspheric. The sixth lens has a specific Abbe's number.