A folding treadmill includes a frame pivotally coupled to a seat, a tread base having a motorized endless treadmill belt and having a front portion pivotally coupled to the frame for allowing the front portion of the tread base to be moved up and down relative to the seat by the frame, and a switching device having one switching member attached to the frame, and another switching member attached to the tread base for selectively switching off the motorized endless treadmill belt when the tread base is moved upwardly to the upward folding position and for preventing the motorized endless treadmill belt from being operated inadvertently and for preventing the users or children from being hurt inadvertently.