Abstract: The present invention provides an all-solid-state type reflection light controllable electrochromic device having a buffer layer, and the constitution thereof comprises an all-solid-state reflective dimming electrochromic device in which a transparent conductive film layer, an ion storage layer, a solid electrolyte layer, a buffer layer, catalyst layer, and a reflective light controllable layer of a magnesium alloy thin film, in particular a multilayer thin film that uses a magnesium-nickel alloy, magnesium-titanium alloy or magnesium-niobium alloy, are formed on a transparent base that uses a glass or resin sheet, and a method for manufacturing the device, and an optical switchable component that incorporates the reflective light controllable electrochromic device, and according to the present invention, a reflective light controllable electrochromic device having a novel multilayer structure can be provided that enables high transmittance when it is transparent and enables switching in a short time over a w