The present invention provides an imaging lens composed of four lenses that can be made compact (downsized, thinned), allows a reduction in cost and is compatible with a high pixel imaging element having a megapixel or more incorporated in a small mobile product such as a mobile phone. The imaging lens 7 includes, in order from the object side to the image surface side: an aperture stop 5; a first lens 1 having positive power; a second lens 2 composed of a meniscus lens having negative power whose lens surface facing the image surface side is concave; a third lens 3 composed of a meniscus lens having positive power whose lens surface facing the image surface side is convex, and a fourth lens 4 having negative power whose lens surfaces are both aspheric and lens surface facing the image surface side is concave in the vicinity of the optical axis. A diffractive optical element is formed on one of the lens surfaces of the first lens 1 or one of the lens surfaces of the second lens 2.