In a waveguide-type optical modulation element that modulates light by applying radio frequency signals to an electrode, the realization of the additional broadening of the bandwidth by improving the degree of freedom in the design of the electrode is enabled. An optical modulation element, which includes optical waveguides provided in a substrate and electrodes that control light waves propagating through the optical waveguides and modulates light by propagating radio frequency signals to the electrodes, in which the electrodes include conductive layers made of copper or a copper alloy and protective layers made of a material other than copper and a copper alloy.