To suitably adjust an optical axis of a headlight by accurately determining the inclination state of a chassis frame without giving influence to a road surface condition by recession/projection of a road surface and rain.

The optical axis adjustment device is provided with a front side clearance detection sensor 36 for detecting a clearance A between a front wheel axle 32 and the chassis frame 11; a rear side clearance detection sensor 37 for detecting a clearance B between a rear wheel axle 34 and the chassis frame; an optical axis adjustment means for adjusting an optical axis angle of the headlight 15; and a controller 20 for controlling the optical axis adjustment means based on a detection output of each detection sensor. The controller calculated an inclination angle α in a longitudinal direction of the chassis frame relative to the road surface by difference of the detection output of the respective clearance detection sensor, calculates weight of a baggage loaded on a load-carrying platform and a center of gravity position from the detection outputs, calculates a deflection angle at a front part of the chassis frame from the weight and the center of gravity position, and controls the optical axis adjustment means based on the sum of the deflection angle and the inclination angle.

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