A cable winding device, comprising: a case comprising a first case element and a second case element; a reel disc disposed between said first case element and said second case element,; a cable wound on said reel disc; and a cable locking structure having a fixing part and at least partially penetrating said first case element and said reel disc;said reel disc is coaxial with said cable locking structure and has a receiving groove arranged around an axial center for receiving at least parts of said cable locking structure, said reel disc further comprises a spiral spring for providing a winding force, an end of said spiral spring is coupled with a spool of said second case element of said case, and said spool is axis of rotation of said reel disc and said spiral spring, characterised in that said reel disc has a leaf spring, the spiral spring being disposed on said receiving groove of said reel disc, a desired length of said cable is pulled out from said case and locked when a pulling operation of said cable causes said leaf spring to be sustained against said fixing part while said fixing part is kept in a fixed height, and said cable pulled outside said case is rewound on said reel disc when said cable locking structure is pressed and said fixing part is detached from said leaf spring; wherein said cable winding device further comprises a deceleration assembly disposed between said first case element and said second case element and connected with said reel disc for decelerating the rotational speed of said reel disc when said cable pulled outside said case is being rewound on said reel disc, and wherein said deceleration assembly comprises a first gear and a second gear, said first gear is coupled with said spool of said second case element of said case and connected with said spiral spring of said reel disc, and said second gear is disposed on an inner surface of said second case element of said case and coupled with said first gear. a case comprising a first case element and a second case element; a reel disc disposed between said first case element and said second case element,; a cable wound on said reel disc; and a cable locking structure having a fixing part and at least partially penetrating said first case element and said reel disc;said reel disc is coaxial with said cable locking structure and has a receiving groove arranged around an axial center for receiving at least parts of said cable locking structure, said reel disc further comprises a spiral spring for providing a winding force, an end of said spiral spring is coupled with a spool of said second case element of said case, and said spool is axis of rotation of said reel disc and said spiral spring, characterised in that said reel disc has a leaf spring, the spiral spring being disposed on said receiving groove of said reel disc, a desired length of said cable is pulled out from said case and locked when a pulling operation of said cable causes said leaf spring to be sustained against said fixing part while said fixing part is kept in a fixed height, and said cable pulled outside said case is rewound on said reel disc when said cable locking structure is pressed and said fixing part is detached from said leaf spring; wherein said cable winding device further comprises a deceleration assembly disposed between said first case element and said second case element and connected with said reel disc for decelerating the rotational speed of said reel disc when said cable pulled outside said case is being rewound on said reel disc, and wherein said deceleration assembly comprises a first gear and a second gear, said first gear is coupled with said spool of said second case element of said case and connected with said spiral spring of said reel disc, and said second gear is disposed on an inner surface of said second case element of said case and coupled with said first gear.