The present invention relates to a composite having exceptional heat resistance and durability that exhibits quick response characteristics when used in an electrochromic device; an electrochromic device in which the composite is used; and a method for producing said composite and device. This composite contains an organic/metallic hybrid polymer that contains an organic ligand and a metal ion coordinated to the organic ligand, and an ionic liquid. The organic/metallic hybrid polymer forms ionic bonds with the ionic liquid. This electrochromic device comprises a first electrode, an electrochromic layer containing the composite, an electrolyte layer, and a second electrode.