The embodiments relate to an electrochromic device having flexibility while achieving an excellent light transmission adjusting function based on the electrochromic principle. The electrochromic device comprises a light transmission variable structure interposed between a first base layer and a second base layer, wherein the light transmission variable structure comprises a first chromic layer and a second chromic layer, the first chromic layer comprises a reducing chromic material, the second chromic layer comprises an oxidizing chromic material, and the value of c as defined in Equation 1 is 1.0 to 1.6.