A microphone contains a capacitor in a capsule with a diaphragm serving as one of electrodes of the capacitor. The microphone is mounted on a mounting board when external terminals installed on an external surface of a circuit board which closes an opening of the capsule are connected face to face with connection terminals on the mounting board. A sound hole is formed in the circuit board and through-hole is formed in the mounting board, being placed in such a position as to avoid overlapping each other when the microphone is mounted. An enclosed space which communicates the through-hole and sound hole is formed when the external terminals are connected with the connection terminals on the mounting board.