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 and is sharply improved in response rate and repeating durability and to provide a film unit with high performance lenses.

The electrochromic diaphragm device is made by holding an electrolyte layer 9 between a pair of transparent electrodes 14, 15 which have a semiconductor nano porous layer 6 formed at least on one side surface thereof and are disposed in such a manner that the semiconductor nano porous layer themselves are opposite to each other and, therein, the diaphragm diameter is made freely changeable by being reversibly changed from a transparent state to an opaque state. Further, in the electrochromic diaphragm device and the film unit with lens using the same, the electrochromic dyestuff 2 which is reversibly colored in black or decolored by at least one of electrochemical oxidation reaction and reduction reaction is included in the electrolyte.