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 second lens, and a third lens. The second lens group includes a fourth lens, a negative fifth lens, and a positive 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 second lens is formed in a shape so that a surface thereof on the image plane side has a negative curvature radius. The fifth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius. The sixth lens is formed in a shape so that surfaces thereof on the object and image plane sides are aspheric.