Abstract: An optical switching unit including mechanisms for receiving a beam of light consisting of a plurality of component rays of different wavelengths, separating the light by making use of the reflection characteristic of suitable spectroscopic elements into the component rays to be lead to corresponding light-conductive paths, selecting either the interruption or transmission of the component rays by means of light-shielding plates provided in the respective light-conductive paths, and collecting the components rays to again compose a composite ray of the beam of light to be let out.The respective light-conductive paths are connected in parallel and have their light-separating branched portions arranged in series. In each of the branched portions is disposed a corresponding one of the spectroscopic elements, which corresponding one has its reflection characteristic reflectable of a corresponding component ray and a component ray reflectable by at least a one-stage preceding spectroscopic element.