An imaging lens includes an aperture stop, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having negative refractive power. Both surfaces of the first lens, both surfaces of the second lens, both surfaces of the third lens, and both surfaces of the fourth lens are formed as aspheric surfaces. The following condition expression (1), condition expression (2), and condition expression (3) are satisfied. - 1.09 ≤ f ⁢ 2 / f ≤ - 0.81 - 1.62 ≤ f ⁢ 2 / f ⁢ 1 ≤ - 1.42 0.65 ≤ f ⁢ 3 / f ≤ 0.97
in which
f1: the focal length of the first lens
f2: the focal length of the second lens
f3: the focal length of the third lens
f: the focal length of the lens whole system