In a holder and a structure for organizing excess length by winding cables and the like, an excess length organizing holder comprises a baseboard which has a rotation axis vertical to a fixed plane, and a spool which has a flange whose edge is provided with two incisions and a winding portion. The spool is rotated around the rotation axis in a state where a cable is folded by way of the winding portion and the two incisions, thereby winding the cable twofold around the winding portion. Also, an excess length organizing structure comprises a door detachable from a box-shaped rack, a mounting hardware connecting the door to the rack and pivoting on one side so as to make the door openable and closable, and at least one excess length organizing holder mentioned above whose baseboard is attached on a surface of the door when the door is attached to the mounting hardware.