A vehicular auto light system is configured to calculate screen brightness on the basis of image data obtained from imaging means that images the outside of a vehicle, operate the imaging means and control imaging conditions with imaging condition control means such that the screen brightness becomes constant, estimate the amount of light around the vehicle with around-vehicle light amount estimating means on the basis of an operation amount of the imaging conditions, and turn lights of the vehicle ON or OFF on the basis of the light amount estimation result.