A light axis adjusting apparatus for a vehicle headlamp has an inclination sensor which receives at least two ultrasonic signals transmitted toward a road surface in a vehicle width direction, and detects the inclined state of a vehicle relative to the road surface based on a receiving time difference between the respective ultrasonic signals. Processings are performed such that the inclination angle .DELTA..alpha. of the vehicle is detected based on the results of detection of the inclination sensor; an actuator is driven based on the inclination angle .DELTA..alpha. to correct the inclination angle of the headlamp; and the abnormality of the inclination sensor is detected based on the state of reception of the ultrasonic signals. Thus, the inclined state of the vehicle is detected constantly with high accuracy, and the light axis of the headlamp can be adjusted appropriately.