An elastic wave device propagating plate waves includes a stack of an acoustic reflection layer, a piezoelectric layer, and IDT electrode on a supporting substrate. The piezoelectric layer is thinner than a period of fingers of the IDT electrode. The acoustic reflection layer includes low-acoustic-impedance layers and high-acoustic-impedance layers. The low-acoustic-impedance layers are made of SiO2, and the high-acoustic-impedance layers are made of at least one material selected from the group consisting of W, LiTaO3, Al2O3, AlN, LiNbO3, SiN, and ZnO.