An imaging lens includes a first lens group having positive refractive power; a second lens group having positive refractive power; and a third lens group having negative refractive power, arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens, and a third lens. The second lens group includes a fourth lens having positive refractive power and a fifth lens having negative refractive power. The third lens group includes a sixth lens and a seventh lens having negative refractive power. The seventh 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 surface of the seventh lens on the image plane side is formed in an aspheric shape having at least one inflexion point.