System for automatically adjusting optical axis direction of vehicle headlight

In a vehicle headlight optical axis automatic adjusting system, a pitch angle (&thetas;p) in the longitudinal direction of a vehicle is calculated from a signal of a height sensor (11, 11F, 11R). Filtering corresponding to a control mode according to the acceleration is fixed and is not frequently switched unless the constant speed state of the vehicle continues for a predetermined time. The pitch angle (&thetas;p) may be calculated on the basis of the vehicle rear height value (HR) by using a prediction expression which is divided into a plurality of regions of vehicle postures according to loading conditions of an occupant load and a trunk load in correspondence with the vehicle type. The pitch angle (&thetas;p) may be updated when the vehicle enters a constant speed driving (stable driving) mode, so that even when one trip is not finished the error is cancelled.