A regulating apparatus for a hydraulic cylinder of a treadmill having a rotating knob with an opening formed at a top end thereof and with a neck formed at a bottom end thereof. The periphery of the neck is marked with a plurality of numbers or with colors from light to dark. An annular base includes a ring-shaped gap for dividing it into an internal and external side. The external side has a viewing window extending to the ring-shaped gap. A magnifying glass is received within the viewing window. Moreover, the internal side of the annular base is fixed atop the hydraulic cylinder. In addition, the rotating knob is fixed on the annular base in such a manner that an adjusting post projects from the opening of the regulating knob and the neck is inserted into the ring-shaped gap. Therefore, the number or the color disposed on the neck is visible from the viewing window when the cushioning force of the hydraulic cylinder is adjusted.
