Provided is a zoom lens system including, in order from an object side to an image side: a first lens unit having a positive optical power; a second lens unit having a negative optical power; a third lens unit having a positive optical power; a fourth lens unit having a negative optical power; and a fifth lens unit having a positive optical power. In this zoom lens system, magnification sharing between the fourth lens unit and the fifth lens unit, and a movement amount of the second lens unit as a principal magnification lens unit are set appropriately, so as to realize a high zoom ratio and high optical performance over an entire zoom range.