An imaging lens includes a first lens having positive refractive power; a second lens; a third lens; a fourth lens; a fifth lens; a sixth lens; and a seventh lens, arranged in this order from an object side to an image plane side with a space between each of the lenses. The second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius. The third 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 a surface thereof on the image plane side has a positive curvature radius. The seventh lens has a specific Abbe's number. The fourth lens and the fifth lens have a specific composite focal length. The sixth lens and the seventh lens have a specific composite focal length.