An acoustic wave device includes first and second acoustic wave elements. The first acoustic wave element is disposed on a piezoelectric substrate, and includes at least one first IDT electrode. The second acoustic wave element is disposed on the piezoelectric substrate, and includes at least one second IDT electrode. The first and second acoustic wave elements are adjacent to each other in the direction of acoustic wave propagation. A diffracting component that diffracts an acoustic wave is disposed between the first IDT electrode and the second IDT electrode. The diffracting component includes a gap that defines and functions as a slit to diffract an acoustic wave.