HEADLIGHT DEVICE

A headlight device (1) provided enables horizontally displacing of the irradiation region (SPOT) for scanning of scanning light (22b) by a light deflector (15b) without problems. The light deflector (15b) includes: a mirror unit that reciprocally turns about first and second rotation axes at first and second frequencies. The first frequency is a natural-oscillation frequency of the mirror unit, and the second frequency is lower than the first frequency. Directions of the first and second rotation axes are set so that scanning directions of the reflected light (23b) due to the reciprocal turning of the mirror unit about the first and second rotation axes are in the directions of vertical axis and horizontal axis, respectively. The control unit (57) controls reciprocal turning of the mirror unit about the second rotation axis based on driving voltage obtained by superimposing offset voltage with basic driving voltage having an increasing and decreasing waveform.