PURPOSE: To provide a small-sized, lightweight, and high performance zoom lens using a refractive index distribution type lens having a refractive index change in the optical axial direction.

CONSTITUTION: This zoom lens has, in order from object side, a first lens group G1 having positive refracting power, a second lens group G2 having negative refracting power, a third lens group G3 having negative or positive refracting power, and a fourth lens group G4 having positive refracting power. At the power variation from wide angle end to telescopic end, the first lens group Gl and the fourth lens group G4 are fixed, the second lens group G2 is monotonously moved from the object side to the image side along the optical axis, and the third lens group G3 is reciprocated along the optical axis. In such a lens, the first lens group G1 has at least one refractive index distribution type lens having a refractive index change in the optical axial direction, and satisfies the condition of -10.6<(ν2--ν1)/[(n2--n1).100]<-0.9.