An extra part draw-in mechanism includes a central axis having a winding face for the flat cable on its outer circumferential face, a rotary body arranged around the central axis and rotatably supported with the central axis at a center of the rotary body, an urging member that urges the rotary body in a winding direction of the flat cable, and a slit that is formed in the central axis and has an opening in the winding face of the central axis to accept and hold the flat cable. The opening of the slit in the winding face of the central axis is curved along a winding direction.