An illumination apparatus that includes a plurality of LEDs of different center emission wavelengths, a photodetector, a path sharing device for introducing light emitted from the plurality of LEDs into the common optical path, a light-introducing device located on the common optical path to introduce part of the light emitted from the plurality of LEDs passing through the common optical path into the photodetector, a feedback controller controlling turning-on states of the LEDs over preset states in accordance with the amount of light emitted from the plurality of LEDs detected by the photodetector, and an illumination light supplying device located on the common optical path to supply light which is emitted from the plurality of LEDs to pass through the common optical path and is not introduced into the photodetector through the light-introducing device, as illumination light for a cellular analysis.