To provide a bio-information acquiring device capable of measuring bio-information such as body motion including respiration, heartbeat, cough, and snore of the organism without marring the freedom of the human body.

The hermetically closed pneumatic sound sensor is composed of an elastic structure 1 deformable by a load, having an opening part 13 and an inner volume, having its opening part closed by applying the load thereto, and formed into a hermetically closed air chamber with the air hermetically closed in its inner volume; an omnidirectional microphone 3 or a pressure sensor detecting the pneumatic pressure therein, and converting it into an electrical signal. The organism information of the body motion including the respiration, the heartbeat, the cough, and the snore of the organism can be detected without marring the freedom of the human body by detecting the pneumatic pressure in a deformable vessel with the organism mounted thereon via a chair, a bed, a toilet lid, a bathtub, and a floor plate.