To provide a diaphragm device capable of accurately detecting the position of a light shielding screen in spite of simple constitution, and thereby capable of saving power by turning off a driving pulse signal (a state for attracting and holding the light shielding screen to a substrate) simultaneously with the detection of an initial position of the light shielding screen and capable of realizing more highly accurate diaphragm control to take a photograph of excellent picture quality.

The light shielding screen 42 on which a dielectric substance to be electrically polarized at a prescribed pitch is formed is arranged on one side of first and second substrates 41, 44 respectively having first optical apertures 41a, 44b for passing a light beam, a band-like electrode 44a for driving the light shielding screen 42 is formed on the second substrate 44 and second optical apertures 41b, 44b which are turned into a passing state or a shielded state in accordance with the position of the light shielding screen 42 are respectively formed on the first and second substrates 41, 44.