PURPOSE: To prevent the deterioration of performance even when coloration and clecoloration are repeated by interposing an iridium oxide layer.

CONSTITUTION: Two transparent substrates 1 and 2 consisting of a glass thin plate are combined with an org. polymer 3 having ≥10-5Ohm-1.cm-1 protonic conductivity at 20°C with the transparent conductive layers 4 and 5 as the combination faces. An electrochromic substance layer 6 of tungsten oxide in contact with the protonic conductive layer 3 is provided on the conductive layer 4 as the combination face of the substrate 1. The substrate 2 is furnished with an iridium oxide layer 7 at the position symmetrical to the layer 6 with respect to the polymer 3. As a result, coloration and decoloration are repeated without shortening the service life of the glass plate.