A treadmill includes a base frame and an one-way damping device. The one-way damping device includes a rotatable braking plate, an one-way clutch, and a resistance unit. The resistance unit is fixedly mounted to the base frame and abuts against the braking plate. The one-way clutch is sleeved on one of two rotating shafts of the base frame, is not engaged with the braking plate when the rotating shafts are rotated in a first rotational direction, and is engaged with the braking plate when the rotating shafts are rotated in a second rotational direction, which in turn drives the braking plate to co-rotate against a frictional force between the braking plate and the resistance unit.