An acoustic wave device includes a piezoelectric layer, the piezoelectric layer being a rotated Y-cut lithium niobate substrate or an X-cut lithium tantalate substrate; an upper conductive layer having a substantially consistent density, on or over the upper surface of the piezoelectric layer; a lower conductive layer having a substantially consistent density, on or below the lower surface of the piezoelectric layer; and a first additional film having a substantially consistent density, wherein at least one of the upper and lower conductive layers is mainly made of ruthenium, chrome, copper, molybdenum, tungsten, tantalum, platinum, rhodium, or iridium, and wherein at least a part of the first additional film is in the resonance region in the plan view, and the density of the first additional film is equal to or less than the density of aluminum.