Provided is a treadmill including a plurality of slats extending in a first direction and arranged in a second direction perpendicular to the first direction. The frame structure supports both ends of each of the plurality of slats to allow the plurality of slats to be movable in the second direction. The frame structure includes a central frame having a top portion having a curved shape. The frame structure further includes a first side frame and a second side frame respectively arranged on both sides of the central frame. A top portion of each of the first and second side frames has a shape corresponding to the curved shape of the central frame.