a magnification varying device for a copying machine in which a variable magnification zoom lens is arranged between an original surface and a photosensitive surface and the copying magnification is varied by moving the movable lens groups , both with respect to the original and photosensitive surfaces and also with respect to one another . one of the movable lens groups is fixed to a slide plate which is movably supported to be slidable in a direction parallel to the optical axis of the zoom lens . the other lens group is slidable on the slide plate relative to the first lens group . a cam plate having a cam surface is arranged along the line of movement of the slide plate . a cam lever is pivotally mounted on the slide plate and has one arm acting as a cam follower engaged with the cam surface and the other end engaged with a pin coupling it to the second lens group .