A light source unit, which is connected to a control unit and an endoscope, radiates a pre-determined light quantity of white light based on a signal from the control unit. The light source unit includes a lamp as a white light source, an infrared cut filter, a light quantity limiting filter, being inserted/removed on an optical path, for limiting light quantity in a pre-determined wavelength region of white light, a filter insertion/removal driving unit for inserting/removing the light quantity limiting filter on an optical path, and a condensing lens for outputting white light. For example, when a transmission rate of a blue band is 100%, the light quantity limiting filter limits transmission rates of other bands to 50%. This improves S/N in discrete spectral image generation with illumination light in a visible light region.
