A flat cable winding device for winding one end side of a flat cable and leading out another end side of the flat cable, the flat cable winding device comprising: a case (3, 3A, 3B) having an insertion hole through which the flat cable is inserted; a central shaft provided in the case and retaining the one end side of the flat cable; a rotating body configured to rotate about the central shaft; and a biasing element configured to bias the rotating body in a winding direction of the flat cable, wherein the rotating body includes a plurality of rollers (5, 5A) arranged along a circumferential direction of the rotating body and configured to slide in a radial direction of the rotating body, wherein at least one of the plurality of rollers (5, 5A) is a reversing roller configured to reverse the flat cable entered from the insertion hole of the case toward the central shaft, and wherein the rotating body includes a plurality of rail portions formed at an upper face of the rotating body, which are radially-arranged about the central shaft as a center and configured to slide each of the plurality of rollers (5, 5A) in a radial direction of the rotating body, each of the plurality of rail portions includes an elongated hole and a circular portion provided at an end of the elongated hole, and the elongated hole includes a pair of locking portions for attaching the plurality of rollers to the rotating body, such that, when the rotating body which is biased by the biasing element is rotated in the winding direction, the flat cable is wound up so as to form an inner winding portion formed by the flat cable wound around the central shaft and an outer winding portion formed by the flat cable wound around outer circumferences of the plurality of rollers (5, 5A), the plurality of rollers (5, 5A) is pushed toward the inner winding portion by the outer winding portion. a case (3, 3A, 3B) having an insertion hole through which the flat cable is inserted; a central shaft provided in the case and retaining the one end side of the flat cable; a rotating body configured to rotate about the central shaft; and a biasing element configured to bias the rotating body in a winding direction of the flat cable, wherein the rotating body includes a plurality of rollers (5, 5A) arranged along a circumferential direction of the rotating body and configured to slide in a radial direction of the rotating body, wherein at least one of the plurality of rollers (5, 5A) is a reversing roller configured to reverse the flat cable entered from the insertion hole of the case toward the central shaft, and wherein the rotating body includes a plurality of rail portions formed at an upper face of the rotating body, which are radially-arranged about the central shaft as a center and configured to slide each of the plurality of rollers (5, 5A) in a radial direction of the rotating body, each of the plurality of rail portions includes an elongated hole and a circular portion provided at an end of the elongated hole, and the elongated hole includes a pair of locking portions for attaching the plurality of rollers to the rotating body, such that, when the rotating body which is biased by the biasing element is rotated in the winding direction, the flat cable is wound up so as to form an inner winding portion formed by the flat cable wound around the central shaft and an outer winding portion formed by the flat cable wound around outer circumferences of the plurality of rollers (5, 5A), the plurality of rollers (5, 5A) is pushed toward the inner winding portion by the outer winding portion.