A treadmill including: a base seat, a first bracket and a second bracket being respectively pivotally mounted on each of two lateral sides of a front section of the base seat, a damper being disposed between a middle section of each second bracket and a rear end of the base seat; and two tread boards, top ends of the first brackets being respectively pivotally connected under front ends of the tread boards, top ends of the second brackets being respectively pivotally connected under middle sections of the tread boards. When treading the tread boards of the treadmill, a forward travel is achieved. Therefore, a user can use the treadmill just like the user naturally steps forward.