An electro-optical element includes a core layer made of an electro-optical material, a clad structure disposed on each of opposite sides of the core layer and configured to form an optical waveguide together with the core layer, and a pair of electrode layers, one of which being disposed on one side of the clad structure and another being disposed on another side of the clad structure. The clad structure includes a first clad layer and a second layer. The second clad layer has a dielectric permittivity larger than that of the first clad layer, and the second clad layer has a thickness thicker than that of the first clad layer.