A microphone unit (1) has a first vibration plate. A support member (6) supports the microphone unit (1). A second vibration plate (5) is fixed to the support member (6) at a predetermined distance from the first vibration plate. An armoring body (2) covers the microphone unit (1), the support member (6) and the second vibration plate (5). A space surrounded by the support member (6), the first vibration plate and the second vibration plate (5) is a closed space (S1) with air kept therein.