A ball retainer includes a chain belt, a hook, and a slot portion. The hook is arranged on the first end of the chain belt. The hook includes a neck portion, a hook body, two leaning protrusions, and a limiting protrusion. The hook body is connected to the neck portion. The two leaning protrusions extend outward along the short side direction of the chain belt toward two sides of the hook body, respectively. The slot portion is arranged on the second end of the chain belt. The slot portion includes a slot, two abutting portions, a connecting portion, and a receiving portion. After the hook is correspondingly engaged with the slot portion, the hook body is accommodated in the slot, the two leaning protrusions correspondingly lean against the two abutting portions, the neck portion leans against the connecting portion, and the limiting protrusion is correspondingly accommodated in the receiving portion.