When the diaphragm of an electroacoustic transducer vibrates, sounds are radiated from the front and rear faces of the diaphragm. These sounds have mutually opposite phases, so that it is necessary to prevent the sound radiated from the rear face from travelling round to the front face side and causing interference. According to the present invention, the rear face of an electroacoustic transducer incorporating a diaphragm is provided with cylindrical protruding ventilation ports that externally radiate the sound radiated from the rear face of the diaphragm. The ends of the ventilation ports are positioned within through-holes of a mounting circuit board in such a manner that the ends thereof are more remote from the diaphragm than a circuit board contact face. The ends of the ventilation ports may be within the through-holes or may externally protrude from the rear face of the circuit board. In this way, isolation from the sound radiated from the front face of the diaphragm can be achieved, thereby preventing interference with the sound radiated from the front face of the diaphragm.