An optical unit having an electrooptical element whose optical properties are changed as a function of a voltage applied thereto to modulate an incident light in response to the applied voltage. The optical unit includes a shielding member for electrically shielding at least a portion thereof which includes the electrooptical element from an external electric field. The shielding member protects the electrooptical element from an influence of an external electric field on an electrooptical effect of the electrooptical element. The shielding member may be an electrically conductive member, such as a metallic casing accommodating the electrooptical element, or an electrically conductive layer covering a housing accommodating the element.