The light deflection device is configured to switch a first reflection position and a second reflection position in at least some region of the reflection part. The first reflection position is a position at which the light irradiated by the irradiation optical system is to be reflected toward the projection optical system so as to be effectively used as a part of a desired light distribution pattern. The second reflection position is a position at which the light irradiated by the irradiation optical system is to be reflected so as not to be effectively used. The detection unit is arranged at a position at which the light reflected at the second reflection position by the light deflection device can be detected.