A lighting device includes a light source disposed inside of a vehicle, an external light sensor that detects illuminance of light outside of the vehicle, and a controller that controls the light source such that a lower light intensity ratio of the light source is set for higher illuminance detected by the external light sensor. The controller performs a light intensity ratio maintaining control that maintains the light intensity ratio of the light source even when the illuminance changes from a low state to a high state during a period from when a change amount of the illuminance exceeds a predetermined value until a predetermined period elapses.