The present invention has as its object to obtain a zoom lens having a high variable power ratio, and having high optical performance which can sufficiently cope with even the use, for example, of a solid state image pickup element having a wide angle of field.In a zoom lens having, in succession from an object side to an image side, a first lens unit L1 of negative optical power, a second lens unit L2 of positive optical power and a third lens unit L3 of positive optical power, wherein the interval between adjacent ones of the lens units is changed to thereby effect focusing, the first lens unit has a negative lens and a positive lens, the second lens unit has a positive lens and a negative lens, the third lens unit has a positive lens, and the object side and image side surfaces of the negative lens G11 of the first lens unit which is most adjacent to the object side are of an aspherical shape.