This invention relates to a zoom lens system that is an object lens for taking images which is independent of an objective lens for a viewfinder, said zoom lens system being less likely to vary in the total length by zooming in spite of having a high zoom ratio and being reduced in the total length under every condition from the wide angle to telephoto settings. To achieve this, the present zoom lens system is made up of a first lens unit having a negative refractive power, a second lens unit having a positive refractive power and a third lens unit having a positive refractive power. In zooming from the wide angle to telephoto end the spaces between the respective lens units are variable, and the present lens system satisfies the following condition:f.sub.B