1. An imaging lens, substantially consisting of a first lens group having a negative and of power an a second lens group having a positive refractive power disposed in order from the object side, wherein: the first lens group is composed of a first group firs lens which is a single lens having a biconcave shape and a negative refractive power; second lens group is composed of a second group first lens having a positive refractive power, an aperture stop, a second group second lens having a positive refractive power, and a second group third lens having a negative refractive power, disposed in order from the object side; the second group second lens and the second group third lens are cemented together to form a cemented lens; and the imaging lens satisfies conditional expressions (1) and (3) given below: 
 31<νd2<55   (1); and 
 0.9 <dt 3/ f< 1.3   (3) where: νd2: the Abbe number of the second group first lens with reference to the d-line; dt3: the thickness of the second group, first lens on the optical axis; and f: the focal length of the entire lens system.