A variable magnification image forming apparatus includes a photosensitive member, a light source, projecting device for forming and projecting on the photosensitive member an image of the original illuminated by the light source, the projecting device including lens system movable in accordance with a magnification of projection selected, a first limiting member for limiting light rays disposed with a fixed positional relation with respect to the lens system, and a second limiting member for limiting light rays in the lens system, the second limiting member being displaceable in a direction different from a direction of an optical axis of the lens system in accordance with magnification change to change the positional relation with respect to the first limiting member.