The present invention relates to a cable-type secondary battery which can be freely transformed, and more specifically, to a cable-type secondary battery having improved flexibility of the battery by preventing wrinkling, which may occur on a thin metal layer included in packaging. According to the present invention, the flexibility of an electrode can be drastically improved by introducing a support layer on at least one surface of a sheet-type external electrode, and the flexibility of the battery can be improved by forming the support layer, which is the outermost layer of the external electrode, and a polymer resin layer inside the packaging from the same material, and by preventing winkling on the thin metal layer included in the packaging by mutually coupling the support layer and the polymer resin layer.