Abstract: A derailleur is provided with locking devices in the form of bands or ratchets around the upper and lower pivoting members of the derailleur to hold the derailleur securely in place during use and thus preventing the bicycle chain from disengaging from the chain sprocket or the chain wheels. The locking devices are activated/deactivted by a hand lever mounted on the handle bar of the bicycle. A cable runs from the hand lever through a spring arrangement to other cables that are connected to the locking devices.