A zoom lens system includes in order from an object side to an image side, a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, a third lens unit having a negative refracting power, and a fourth lens unit having a positive refracting power. At the time of zooming from a wide angle end to a telephoto end, distances between the lens units change by at least the first lens unit, the second lens unit, and the third lens unit being moved. The second lens unit includes in order from the object side, a first sub-unit having a positive refracting power, a second sub-unit having a negative refracting power, and a third sub-unit having a positive refracting power. A surface on the object side and a surface on an image side of each of the first sub-unit, the second sub-unit, and the third sub-unit are in contact with air, and (the zoom lens system) satisfies the following conditional expression (1). 3.2