A zoom lens includes a first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group including a first sub-lens group having a positive refractive power, an iris, and a second sub-lens group having a positive refractive power; and a fourth lens group having a positive refractive power, wherein the first to fourth lens groups are sequentially arranged from an object side to an image side, the distance between each of the first through fourth lens groups changes when zooming, the surface of the lens closest to the image side in the first sub-lens group is concave, the lens closest to the object side in the second sub-lens group is a meniscus lens concave towards the object side, and the lens located closest to the object side in the third lens group is an aspheric lens.