The invention relates to a small-format, low-cost zoom lens that can gain sufficient telecentricity and aberration performance even with the use of an inexpensive vitreous material, and so lends itself to an electronic image pickup device. The zoom lens comprises a first lens group G1 of negative refracting power, a second lens group G2 of positive refracting power and a third lens group G3 of positive refracting power. For zooming, the lens groups are moved with a change in the spacing between adjacent lens groups. The second lens group G2 comprises a first lens of positive refracting power, a second lens of positive refracting power and a third lens group of negative refracting power, and has three lenses in all. The third lens group G3 comprises a positive lens that is of meniscus shape convex toward an image plane of the zoom lens system and satisfies condition (3), n.ltoreq.1.53.