To provide an image forming lens whose F number is small and which can form a bright image.

The image forming lens is constituted by arranging a first group G1 including one positive refracting lens 10 in which a diffraction lens surface is formed on the lens surface 10b of an image side and a second group G2 which is provided with parallel flat plates 10 and 21 and which is hardly provided with power in order from an object side. The lens 10 of the group G1 is constituted as a positive meniscus lens whose both surfaces are spherical and which is convex to the object side. Besides, the first surface thereof on the object side is spherical and provided with action for correcting astigmatism. The second surface thereof on the image side is spherical and provided with action for correcting a spherical aberration and the high-level curvature of an image surface. At this time, the lens 10 satisfies the condition of 0.64<r1×r2/ f(n1-1)2×d1<1.60. Provided that, r1 and r2 are the radiuses of the curvature of the first and the second surfaces of the lens 10, (f) is the focal distance of the whole system and n1 and d1 are the refractive index and the lens thickness of the lens 10 respectively.