A lens assembly includes a third lens group frame having an end face extending in an optical-axis direction and provided with an end-face cam having displacement along a peripheral direction, for retaining a third group of lenses, a second lens group frame having a cam follower abutted against the end-face cam for retaining a second group of lenses, a second lens group spring for biasing the second lens group frame toward the third lens group frame, rotational regulator for regulating rotation of one of the third lens group frame and the second lens group frame around an optical axis, and a rotator for rotating the other of the third lens group frame and the second lens group frame around an optical axis when zoom operation is performed, wherein the end-face cam and a cam follower are operated by relative angular movement of the third lens group frame and the second lens group frame, around the optical axis at the time the zoom operation is performed to modify spacing therebetween in the optical-axis direction.