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 positive first lens, a positive second lens, and a negative third lens. The second lens group includes a fourth lens, a fifth lens, and a sixth lens. The first lens is formed in a shape so that surfaces thereof on the object and image plane sides have positive curvature radii. The fifth lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius. 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 first to third lenses are arranged specifically and have specific Abbe's numbers.