A zoom lens in which a precise focus detection signal can be detected while a user can observe an image to be shoot without being affected by insertion/removal of an extender lens into an optical axis. A relay lens unit stationary during zooming includes lens unit L21 including a branch element, lens unit L22 interchangeable with extender lens unit insertable into/removable from optical path to change focal length range of the entire system and positive lens unit L23 in order from object side to image side, and the zoom lens satisfies specific conditions among distance from an aperture stop to front principal point of L21, distance from rear principal point of L21 to front principal point of L22, distance from rear principal point of L22 to front principal point of L23, refractive power of L21, and refractive power of the entire system of the zoom lens at wide-angle end.