To provide an in-car lighting system with illumination in a usual time also serving as illumination when electric power is interrupted.

The in-car lighting system includes an electric power source for illumination, a battery for the electric power interruption, an illumination unit comprising a plurality of LEDs supplied selectively with an output of the battery for the electric power interruption or the electric power source for the illumination, a power interruption detection switching circuit for monitoring the electric power source for the illumination, and for supplying the output of the battery for the electric power interruption, to the illumination unit, when detecting the power interruption in the electric power source for the illumination. In the illumination unit, the plurality of LEDs turns on when electric power is supplied from the electric power source for the illumination, and part of LEDs out of the plurality of LEDs turns on when the output of the battery for the electric power interruption is supplied.