An acoustic sensor includes a semiconductor substrate with a back chamber, a conductive diaphragm arranged on an upper side of the semiconductor substrate, an insulating fixed film fixed on an upper surface of the semiconductor substrate covering the conductive diaphragm with a gap, a conductive fixed electrode film arranged on the insulating fixed film facing the diaphragm, an extraction wiring extracted from the conductive fixed electrode film, and an electrode pad to which the extraction wiring is connected. The acoustic sensor converts an acoustic vibration to change electrostatic capacitance between the conductive diaphragm and the conductive fixed electrode film. A plurality of acoustic perforations are opened in a back plate including the insulating fixed film and the conductive fixed electrode film. An opening rate of the plurality of acoustic perforations is smaller in the extraction wiring and a region in the vicinity thereof than in other regions.