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

The electrochromic diaphragm device is made by holding an electrolyte layer 9 between a pair of transparent electrodes 14a, 15a which have a semiconductor nano porous layer of specific surface area of 1-5,000 m2/g formed on at least one side surface thereof and are disposed in such a manner that the semiconductor nano porous layers 4, 6 themselves are opposite to each other and can change the diaphragm diameter freely by reversibly being changed from a transparent state to an opaque state. Thereby in the electrochromic diaphragm device and the film unit with lenses using the same, at least one kind of electrochromic dyestuff 2 which reversibly is colored or decolored by at least one of electrochemical oxidation reaction or reduction reaction is contained in the electrolyte.