An electret condenser includes a fixed film 110 including a conductive film 118 to be an upper electrode, a vibrating film 112 including a lower electrode 104 and a silicon oxide film 105 to be an electret film, and a silicon oxide film 108 provided between the fixed film 110 and the vibrating film 112 and including an air gap 109. Respective parts of the fixed film 110 and the vibrating film 112 exposed in the air gap 109 are formed of silicon nitride films 106 and 114.