A flexible secondary battery includes an electrode support; a sheet-type internal electrode wound helically outside of the electrode support; a sheet-type first solid electrolyte layer wound helically outside of the internal electrode; a sheet-type bipolar electrode wound helically outside of the first solid electrolyte layer; a sheet-type second solid electrolyte layer wound helically outside of the bipolar electrode; and a sheet-type external electrode wound helically outside of the second solid electrolyte layer, wherein each of the first and second solid electrolyte layers include an organic solid electrolyte, the internal electrode is provided with insulation coating portions at both longitudinal ends of one surface facing the first solid electrolyte layer, the external electrode is provided with insulation coating portions at both longitudinal ends of one surface facing the second solid electrolyte layer, and the bipolar electrode is provided with insulation coating portions at both longitudinal ends of both surfaces.