<p>A light control element which suppresses entry of non guided light into a light guide and has excellent optical characteristics such as a light modulation characteristic. The light control element, which includes a substrate formed of a material having electrooptical effects and the light guide formed on the front plane or the rear plane of the substrate, is characterized in that propagation constants (ß<SUB>0</SUB>-ß<SUB>3</SUB>) of the light guide are set at different values by part. Preferably, the light control element is characterized in that the propagation constants of the light guide are different from those relating to the non guided light which propagates outside the light guide.</p>
