Described is an optical element having plural electrodes and, disposed therebetween, a stimuli-responsive polymer gel, a liquid which can be absorbed therein and an ion supplying material. As the ion supplying material, preferred is a material showing a volumetric change, in the form of the element, of 0 to 100% under external stimuli. According to the present invention, a novel optical element showing a large change in light transmittance, reflectance or absorption amount and exhibits stable optical properties in repetition can be provided.