A zoom lens system, which has a high zoom ratio while having a high optical performance, includes, 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, and a fourth lens unit having a positive optical power. The second lens unit and the fourth lens unit move during zooming. Lens elements constituting the first lens unit and the second lens unit are appropriately set.