To provide an electrochromic diaphragm device which is suitable for a photographing device of camera, etc., in particular, a diaphragm device, etc., of a camera with lenses, is easily miniaturized and is sharply improved in response rate and repeating durability and to provide a film unit with high performance lenses using the electrochromic diaphragm device.

The electrochromic diaphragm device is constituted by laminating plural sheets of structural units made by holding an electrolyte layer containing an electrochromic dyestuff reversibly colored and decolored by using at least one of electrochemical oxidation reaction and reduction reaction between a pair of transparent electrodes which have a semiconductor nano porous layer formed on at least one side surface thereof and are disposed in such a manner that the semiconductor nano porous layer themselves are opposite to each other. Thereby in the electrochromic diaphragm device and the film unit with lenses using the same, the diaphragm diameter is made freely changeable by reversibly changing the structural units from the transparent state to the opaque state.