The automotive headlamp unit having a lamp housing formed integrally with a front lens and in which a reflector and a lamp bulb as a light source are provided is provided with an aiming adjustment device including pivot mechanisms to tilt the lamp housing about horizontal and vertical axis, respectively, in relation to the body of a car, and also the lamp housing has provided therein an aiming adjustment aid composed of a level vial supported tiltably in the vertical plane parallel to the optical axis of the reflector and a manual operating member to adjust the tilt angle of the level vial. At the headlamp unit manufacturer, the posture of the lamp housing with respect to the car body is pre-adjusted by means of the aiming adjustment device to obtain an optimum luminous intensity distribution pattern, and in this adjusted condition, the level vial is tilted in the vertical plane parallel to the optical axis by means of the manual operating member until the bubble in the level vial comes to the reference position at the center of the level vial. This condition is held. This tilt angle of the lamp housing corresponding to the optimum orientation of the optical axis with respect to the plane of the ground is easily reproduced, and so the aiming adjustment of the headlamp unit can be very easily done at the automobile manufacturer or car repair/maintenance shop.