An input device includes a casing, a base member, a ball member, a control ring and a gravity wheel. The casing includes an upper cover and a lower cover. The upper cover has an opening. The ball member is installed on the base member. The ball member is partially exposed outside the opening. The control ring is arranged around the base member. The control ring is partially exposed outside the opening. The control ring is freely rotatable around the base member. The control ring includes a first inclined part, a rack structure, and a lateral wall. The lateral wall is connected with the first inclined part and the rack structure. The gravity wheel is engaged with the rack structure. Consequently, the rotation of the control ring is suppressed by the gravity wheel.