PURPOSE: To obtain a compact zoom lens having a high variable power ratio by arranging at least one distributed index lens having the refractive index distribution in the direction of the optical axis in one lens group of a lens system where intervals among three lens groups are changed for zooming.

CONSTITUTION: A lens system consists of a first lens group I having a positive refracting power, a second lens group II having a positive refracting power, and a third lens group III having a negative refracting power in order from the object side. In this lens system where firstWthird lens groups IWIII are moved to the object side on the optical axis in case of zooming based on the wide angle end to the telephoto end, at least one axial type distributed index lens having the refractive index distribution in the direction of the optical axis is arranged in at least one lens group. That is, the second lens (the image-side lens of a cemented lens) from the object side in the first lens group I is the axial type distributed index lens. Thus, the compact zoom lens having a satisfactory optical performance is realized because aberrations in each lens group are reduced in spite of a high variable power ratio.