The present invention relates to a display device utilizing an electrochemically reversible coloring reaction and, more specifically, to an electrochromic display device (referred to as ECD hereinafter) which makes it possible to carry out a stable display to appearing-disappearing performance using an iron compound insoluble to an electrolyte as an electrochemical reactant to a counter electrode. In order to operate an ECD stably, it is necessary to stabilize the electro-potential applied to the counter electrode. The ECD of the invention is characterized by using iron berlinate or derivatives thereof as a potential stabilizing material of the counter electrode, and the ECD is constructed with a display electrode and a counter electrode provided with the said compound as a reactive component thereon, thereby making it possible to maintain a stably display function. Furthermore the invention relates also to an ECD using a solid thin film of an electrochromic substance as a display electrode, in which lithium fluoborate is used as a supporting substance of the electrolyte and water is added to the electrolyte in a concentration of 0.1 to 2 Mol/l, thereby improving the temperature performance and response speed of the ECD without affecting its working life thereof.