ACOUSTIC WAVE DEVICE

An acoustic wave device includes an Interdigital Transducer (IDT) electrode on a first main surface of a piezoelectric layer, a conductive material layer on a second main surface of the piezoelectric layer, and a dielectric layer provided between the piezoelectric layer and the conductive material layer. When a film thickness of the piezoelectric layer is represented as Tp[λ] and a film thickness of the dielectric layer is represented as Td[λ], the Formula (1) is satisfied or Td=0, where λ is a wavelength determined by an electrode finger pitch of the IDT electrode, and Tp[λ]≥about 0.025:Td[λ]≤−2.369×(Tp[λ])4+2.721×(Tp[λ])3−1.049×(Tp[λ])2+0.076×(Tp[λ])+0.095 Formula (1).