An elastic boundary wave device includes a LiNbO3 substrate, an electrode exciting an elastic wave and provided on the substrate, and a silicon oxide film provided on the substrate to cover the electrode, and parameters of the elastic boundary wave device have any one of ranges, where “θ” is a rotation Y cut angle of the substrate, “a” is a ratio of copper density with respect to a density of a material used as the electrode, “λ” is a wavelength of the elastic wave excited by the electrode, “h” is a film thickness of the electrode, “H” is a thickness of the silicon oxide film.