A light source apparatus that generates a light to be supplied to an endoscope, which includes: LEDs of respective colors that emit lights； collimator lenses that receive emitted lights and emit the received lights； and illuminance sensors arranged at positions where the illuminance sensors can receive both of leak lights of the lights emitted from the LEDs of respective colors, which are not used as illumination lights, and lights emitted from the LEDs of respective colors and reflected by the collimator lenses.
