Provided is a technique by which, when excessive pressure acts on an acoustic sensor, an increase in pressure in a casing is prevented to suppress excessive transformation of a vibration electrode film caused by the increased pressure. An acoustic sensor is provided with: a substrate; a back plate having sound holes that allow passage of air; a vibration electrode film disposed so as to face the back plate; and a package 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 is further provided with a projection configured to block a flow path for air (inhibit a flow of air) that passes through a gap between the vibration electrode film and the back plate, and a sound hole, when the vibration electrode film is transformed to come close to the back plate.