PURPOSE: To obtain an ECD oxidation coloring layer having high performance and reproducibility by using nickel oxyhydroxide for the oxidation coloring layer of a fully solid state electrochromic element having reduction coloring, diaphragm and oxidation coloring layers between electrodes.

CONSTITUTION: A transparent electrode (ITO or "NESA") 2 is formed on a transparent substrate 1 such as glass substrate. An NiOx(OH)y film layer 3 is formed on the electrode 2. An electron blocking diaphragm layer 4 of a good proton conductor consisting of SiOx, Ta2O5, etc. and a reduction coloring layer 5 of WO3, etc. are successively laminated on the layer 3 and finally transparent conductive films 6aW6d formed at a low temp. (≤150°C) by a technique such as reactive ion plating or the like are laminated thereon. Protective layers 7aW7e are provided thereon as well. The NiOx(OH)y film is formed by a sputtering device.