To provide an electret capacitor microphone that can be reduced sufficiently in thickness.

This capacitor microphone is constituted in such a way that a capacitor section C composed of a diaphragm 26 and a back pole plate 18 which are faced to each other through a spacer 16 is housed in the cylindrical case 12 with the diaphragm 26 upside. The upper end of the case 12 is constituted of an end face wall 12b having an opening 12a for tone hole and the lower end of case 12 is opened. In the case 12, in addition, a JFET board 24 is housed below the capacitor section C with the JFET chip 34 of the board 24 upside. A communicative opening 42A which communicates the spaces on both sides of the pole plate 18 with each other and has a larger area than the upper end section of the chip 34 has is formed through the pole plate 18 at the position facing the chip 34. Consequently, even when a clearance which is larger than the height of the chip 34 by a certain degree is not secured between the pole plate 18 and the board main body 32 of the board 23 unlike the conventional example in which the clearance is secured, the interference between the chip 34 and plate 18 can be prevented.