A vehicle headlight apparatus, on a vehicle applies illumination light to a road surface, comprises: a light source device to generate the illumination light; and a lens on a light axis of the light source device and projects the illumination light from the light source device to form a desired light distribution, wherein the light source device includes: one or more semiconductor light source elements to emit light; a collimator unit having one or more collimators disposed on a light emission axis of each of the semiconductor light source elements and converts light emitted from a solid light source into substantially parallel light; and a polarization conversion element provided on an emission surface side of the collimator unit and converts incident light into predetermined polarized light, and the illumination light emitted from the polarization conversion element of the light source device is applied in a predetermined direction through the lens.