A zoom lens system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. The third lens unit is stationary and the second and fourth lens units move along an optical axis during zooming. The fourth lens unit consists of a cemented lens in which a positive lens element and a negative lens element are cemented together. The zoom lens system satisfies the following conditional expression: 7.5