The present invention provides a condenser microphone capable of detecting small sounds (e.g., Korotkoff sounds) with high sensitivity even in environments with variations in pressure, such as cuff pressure. A condenser microphone (10) is disposed as an acoustic sensor for detecting Korotkoff sounds in a communication space reachable by the internal pressure of the cuff of a blood pressure gauge. In the condenser microphone, a diaphragm (13) and a backplate 14) are disposed in the interior of a housing (11), an aeration hole (30) is formed in a wall (11B) that blocks off the housing back surface, and a sound-absorbing element (20) having sound absorption characteristics with respect to a frequency band targeted for detection is disposed on the front surface of a housing (11).