The present invention relates to an adjusting apparatus having an optical aimer that includes a reflector for adjusting parts of a motor vehicle, in particular distance warning radar, headlights, or an axle; having an emitting device that emits a collimated beam; and having a vertical adjusting device for orienting the reflector at a certain angle to a floor of a measuring station forming the contact plane of the vehicle. An exact vertical alignment or orientation at a certain tilt angle to the floor of the measuring station is achieved by simple measures, in that the emitting device is positioned in a vehicle region remote from the aimer, at a specific, defined level of the vehicle above the measuring-station floor and may be adjusted for emitting the beam at different elevation angles relative to a line parallel to the measuring-station floor, and the vertical adjusting device has a diaphragm unit, which is situated between the aimer and the emitting device and has a vertically adjustable diaphragm, whose level is adjustable in such a manner that the beam directed at the reflector and passing through the diaphragm passes through it again after being reflected at the reflector.