To provide an electrochromic diaphragm device which is adequate as a diaphragm device, etc., of a photographic device, such as a camera, more particularly a camera with a lens, can be easily downsized and greatly improved in a response speed and repeating durability and a high-performance film unit with a lens using the same.

The electrochromic diaphragm device is formed by holding an electrolyte layer 9 between a pair of transparent electrodes 14a and 15a formed with semiconductor nano-porous layers on at least one surface and arranged to allow the semiconductor nano-porous layers 4 and 6 to face each other and can freely change a diaphragm aperture by reversibly changing the electrolyte layer from a transparent state to a translucent state. The electrochromic diaphragm device comprising incorporating at least one electrochromic dyestuffs reversibly colored or decolored by an electrochemical oxidation reaction or reduction reaction into the electrolyte and the film unit with the lens using the same.