A cord winder includes a base, a rotating disc, a spiral spring, a cord, a cord positioning element, a push button, and a top cover. When a first end part of the cord is pulled, the rotating disc and the cord positioning element are rotated in a first direction, and two protruding blocks of the push button are moved along an inner surface of the cord positioning element. When the first end part of the cord is no longer pulled, the two protruding blocks are respectively contacted with two notches of the inner surface of the cord positioning element. Consequently, the rotating disc and the cord positioning element are not rotated. When the push button is pressed down, the rotating disc and the cord positioning element are rotated in a second direction in response to a restoring force of the spiral spring. Consequently, the cord is retracted back.