A capacitive transducer, comprising: a substrate having an opening in a surface thereof; a back plate (7, 17, 27, 37, 47) facing the opening in the substrate; a vibration electrode film (5, 15, 25, 35, 45) facing the back plate (7, 17, 27, 37, 47) across a space, the vibration electrode film (5, 15, 25, 35, 45) being displaceable to have a displacement converted into a change in capacitance between the vibration electrode film (5, 15, 25, 35, 45) and the back plate (7, 17, 27, 37, 47); an airflow channel defined by a gap between a protrusion (17b, 27b, 37b, 47b) integral with the back plate (7, 17, 27, 37, 47) and a part of the vibration electrode film, the airflow channel being configured to increase an area of air flow when the vibration electrode film (5, 15, 25, 35, 45) deforms under pressure to move relative to the protrusion (17b, 27b, 37b, 47b) integral with the back plate (7, 17, 27, 37, 47) and relieve the pressure applied to the vibration electrode film (5, 15, 25, 35, 45) to serve as a pressure relief channel; and an extension (15d, 25d, 35d) formed at a periphery of a hole (15b, 25b, 35b, 45b) in the vibration electrode film (5, 15, 25, 35, 45) defining the pressure relief channel, the extension (15d, 25d, 35d) including a slit (15c, 25c, 35c) increasing an area of the airflow channel in the hole (15b, 25b, 35b, 45b), wherein the protrusion (17b, 27b, 37b, 47b) integral with the back plate (7, 17, 27, 37, 47) passes through the hole (15b, 25b, 35b, 45b) in the vibration electrode film (5, 15, 25, 35, 45) when the vibration electrode film (5, 15, 25, 35, 45) is in a resting position. a substrate having an opening in a surface thereof; a back plate (7, 17, 27, 37, 47) facing the opening in the substrate; a vibration electrode film (5, 15, 25, 35, 45) facing the back plate (7, 17, 27, 37, 47) across a space, the vibration electrode film (5, 15, 25, 35, 45) being displaceable to have a displacement converted into a change in capacitance between the vibration electrode film (5, 15, 25, 35, 45) and the back plate (7, 17, 27, 37, 47); an airflow channel defined by a gap between a protrusion (17b, 27b, 37b, 47b) integral with the back plate (7, 17, 27, 37, 47) and a part of the vibration electrode film, the airflow channel being configured to increase an area of air flow when the vibration electrode film (5, 15, 25, 35, 45) deforms under pressure to move relative to the protrusion (17b, 27b, 37b, 47b) integral with the back plate (7, 17, 27, 37, 47) and relieve the pressure applied to the vibration electrode film (5, 15, 25, 35, 45) to serve as a pressure relief channel; and an extension (15d, 25d, 35d) formed at a periphery of a hole (15b, 25b, 35b, 45b) in the vibration electrode film (5, 15, 25, 35, 45) defining the pressure relief channel, the extension (15d, 25d, 35d) including a slit (15c, 25c, 35c) increasing an area of the airflow channel in the hole (15b, 25b, 35b, 45b), wherein the protrusion (17b, 27b, 37b, 47b) integral with the back plate (7, 17, 27, 37, 47) passes through the hole (15b, 25b, 35b, 45b) in the vibration electrode film (5, 15, 25, 35, 45) when the vibration electrode film (5, 15, 25, 35, 45) is in a resting position.