An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens; a fourth lens having negative refractive power; a fifth lens having positive refractive power; and a sixth lens, arranged in this order from an object side to an image plane side. The first lens is formed so that a surface thereof on the object side has a positive curvature radius. The sixth lens is formed so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii. Each of the first to sixth lenses has an Abbe's number within a specific range.