An acoustic wave element includes an IDT electrode in contact with a piezoelectric material and including a plurality of electrode fingers, which include first and second electrode fingers that adjoin each other in an acoustic wave propagation direction and that connect to different potentials and a first dummy electrode finger facing the first electrode finger via a gap located on an outer side in an electrode finger length direction of the first electrode finger. At an area near the gap, first protrusions are provided in at least one of the first electrode finger and the first dummy electrode finger, the first protrusion protruding in the acoustic wave propagation direction from at least one of side edges of the at least one of the first electrode finger and the first dummy electrode finger. The acoustic wave element has greatly improved resonance characteristics of a resonance frequency and prevents short-circuit failure between electrode fingers and degradation in insulation properties.