it is possible to freely design such as for example arranging on a straight line also conventionally since two biasing springs have been used i e one at the movable member and one at the base member in order to absorb the sag of the chain 18 it has been very troublesome to set design the interrelationships among these spring forces in this rear derailleur 172 however since only a single biasing spring 242 has been used i e at the movable member 22 it is not necessary to take relative spring forces into account but it is relatively easy to design and it is also easy to manufacture and assemble the rear derailleur 172 itself this second embodiment is substantially identical to the first embodiment thus like reference numerals will be used for like parts herein the control cable is frequently used in combination with a guide tube in which the control cable has been inserted when such a control cable is used the cable pulley 251 becomes unnecessary a rear derailleur 172 of the second embodiment shown in fig1 is an example in which a control cable with guide tube has been used end portions of the guide tube 253 is inserted and fixed in seats provided at each of the frame 11 and a protruded portion 213 of the base member 21 and the control cable 25 is inserted into through the guide tube 253 since this embodiment is the same as in the first embodiments with the exception of the foregoing explanation concerning the structure operation and effect of the modifications of.