Abstract: An illuminating device including a cylindrical main body that is provided with a circularly arranged plurality of LEDs of different colors so as to be used in, for instance, an optical inspection apparatus. The illuminating device further includes a light diffusing element, light-condensing lens and a polarizing element or a prism having polarizing surfaces, which are all installed inside the cylindrical main body. The LED lights are corrected in intensity to be even by the light-diffusing element, pass through the light-condensing lens and further pass through the prism so as to be directed toward a single point and form a superimposed light illuminating an object, thus a CCD camera that is provided in the center of the cylindrical main body can take an image of the object.