An acoustic device includes: a perforated plate that has a plurality of holes penetrating in a plate thickness direction of the perforated plate and in which a main flow is to flow on a first side of the perforated plate in the plate thickness direction; and a housing that is on a second side of the perforated plate in the plate thickness direction and partitions a space between the housing and the perforated plate, wherein a part of each of the plurality of holes on the first side in the thickness direction is inclined to at least one of the first side and a second side of a flow direction of the main flow.