PURPOSE: To simply and promptly carry out the adjustment of the optical axis of a head-light with a high degree of accuracy without errors, by comparatively judging whether the voltage falls between an upper limit voltage and a lower limit voltage or not, so that the operation of a device for driving the optical axis of the head-light is stopped when the voltage falls therebetween.

CONSTITUTION: A motor 1 is rotated, normally or reversely in dependence upon the direction of energization, so that the optical axis of an optical axis driving device 2 for an head-light is changed upward or downward. A window comparator 5 receives output voltages VH, VL, as upper and lower limit reference voltages VRH, VRL, from a reference voltage setting device 4, and as well receives an output voltage VO, as an input voltage VIN, from an optical axis detector 3. In accordance with output signals from the window comparator 5, a motor control circuit 7 allow the motor 1 to rotate, normally or reversely. If the input voltage VIN is higher (lower) than the upper (lower) limit reference voltage VRH (VRL), a comparator 5a (5b) is turned on to make the output high, but the output voltage becomes low in the case other than the above-mentioned case.