In an acoustic wave device, an interdigital transducer electrode is disposed on a piezoelectric substrate with a reverse velocity surface having an elliptic shape, and a dielectric film is disposed to cover the interdigital transducer electrode. Assuming an electrode density (%) of the interdigital transducer electrode to be y (%) and a wavelength-normalized film thickness 100h/λ (%) of the interdigital transducer electrode to be x (%), the wavelength-normalized film thickness x of the interdigital transducer electrode takes a value not less than x satisfying y=0.3452x2−6.0964x+36.262 depending on the electrode density of the interdigital transducer electrode.