A diaphragm for use as a pressure receiving and dislocatable member in a condenser-type microphone detector. The diaphragm electrode is a thin metallic film member having a central movable portion, a supporting frame portion around the outside of and spaced from the central movable portion, and at least three supporting spring portions at equal intervals around the periphery of the central movable portion and connected between the central movable portion and the supporting frame portion for permitting the central movable portion to be moved out of the plane of the supporting frame portion by differential pressure across the opposite sides of the central movable portion. The central movable portions can have holes therein for partly relieving the pressure thereon.