Disclosed herein is an electrochromic device having a structure in which atoms of an electrolytic layer and an ion storage layer are mixed with each other. The electrochromic device includes an active layer configured to provide a transparent state by a protonation and a reflective state by a deprotonation, an ion storage layer which stores a proton, an electrolytic layer which is provided between the active layer and the ion storage layer and used a medium through which the proton is moved, and a mixed layer having constituent elements of the ion storage layer and the electrolytic layer.