An acoustic wave device includes a piezoelectric board including a piezoelectric layer with a first principal surface and a second principal surface opposed to each other, an intermediate layer on the first principal surface or the second principal surface of the piezoelectric layer, and a functional electrode on the intermediate layer. A material of the intermediate layer is a same type as a material of the piezoelectric layer, and an electromechanical coupling coefficient of the intermediate layer is smaller than an electromechanical coupling coefficient of the piezoelectric layer.