A treadmill includes a handle device disposed on a seat, a tread base rotatable between a downward working position and an upward folding position. Two arms and two levers and two bars are pivotally secured between the tread base and the seat, for allowing the tread base to be rotated relative to the seat. A tube may be secured to the arms, a bolt is threaded with the tube, and a motor may be coupled to the bolt for rotating the bolt to move the tube away from and toward the bolt, and thus to rotate the tread base between the downward working position and the upward folding positions.