A stretchable flexible substrate includes a film base. At least a portion of the film base includes a rolled part. The rolled part includes a first curved part having a curved shape in which the film base is folded back with one main surface of the film base facing inward, a second curved part having a curved shape in which the film base is folded back with another main surface of the film base facing inward, and a base layered part located outside the first curved part and the second curved part. The base layered part has a shape in which the film base is rolled in such a way that a portion of the film base that is contiguous with the first curved part and another portion of the film base that is contiguous with the second curved part are layered on one another.