To provide an auto-leveling system of a vehicular lamp capable of properly controlling a radiant light axis even when a vehicular pitch angle is changed by sudden breaking operation or sudden acceleration operation during traveling of the vehicle.

In the auto-leveling system, an ECU 1 for vertically changing and controlling a radiant light axis of a lamp HL according to a vehicular pitch angle is equipped with a responsiveness varying means (filter part) 105 capable of varying responsiveness of change/control of the radiation light axis with respect to the change of the pitch angle. The control part 101 quickens the responsiveness of the filter part 105 only for a predetermined time when the pitch angle changes for not less than the predetermined angle. The radiation light axis of the lamp HL is quickly controlled by leveling when the front part of the vehicle body is significantly leaned forward or backward by acceleration operation or breaking operation. Thus, dazzling to other cars can be protected, and driver's forward distant visibility is secured.