An acoustic sensor has a semiconductor substrate having an opening, a back plate that is disposed facing the opening of the semiconductor substrate, that is configured to function as a fixed electrode, and that has sound holes that allow passage of air, a vibration electrode film disposed facing the back plate through a void, and a casing configured to house the substrate, the back plate, and the vibration electrode film, and having a pressure hole that allows inflow of air. The acoustic sensor converts transformation of the vibration electrode film into a change in capacitance between the vibration electrode film and the back plate to detect sound pressure.