The present invention provides an imaging lens composed of three lenses that can be made compact (downsized, thinned), allows a reduction in cost and can be made 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 6 includes, in order from the object side to the image surface side: an aperture stop 4; a first lens 1 having positive refractive power whose lens surface facing the image surface side is provided with a diffractive optical element; a second lens 2 composed of a meniscus lens having positive refractive power whose lens surface facing the image surface side is convex; a third lens 3 having negative refractive power. When f denotes the focal length of the entire optical system, f1 denotes the focal length of the first lens 1, f2 denotes the focal length of the second lens 2, f3 denotes the focal length of the third lens 3 and φDOE denotes refractive power of the diffractive optical element, conditional expressions (1) to (4) are satisfied: 0.9