An acoustic sensor adapted to convert acoustic vibration to a change in an electrostatic capacitance to detect the acoustic vibration is provided. The acoustic sensor includes a semiconductor substrate, a back plate including a fixed plate arranged to face a surface of the semiconductor substrate, and a fixed electrode film arranged on the fixed plate, and a vibrating electrode film arranged to face the back plate with a space formed therebetween. The vibrating electrode film includes a plate-like vibrating member that vibrates in response to sound pressure. The vibrating electrode film is fixed to the back plate with a fixing unit thereof including one or more fixing portions each including a fixing protruding end that is arranged on a protruding end of a leg portion protruding from an edge of the vibrating member. The vibrating member has an edge portion surrounding at least a part of the fixing protruding end.