Bicycle derailleur having an improved mechanism for swinging a chain guide

A bicycle derailleur for shifting a driving chain to a selected one of a plurality of axially aligned sprockets forming a multistage sprocket assembly, said derailleur comprising:

• a fixing member;
• a supporting member swingably supported to said fixing member by a first vertical shaft, said supporting member being swingable to move along the direction of the axes of said sprockets around said first vertical shaft;
• a return spring interposed between said fixing member and said supporting member for biasing said supporting member relative to said fixing member;
• a change-over frame swingably supported to said supporting member by a second horizontal shaft, said second shaft having its axis perpendicularly intersecting the axis of said first shaft and being disposed at the position where an extension line of the axis of said first shaft passes through the axis of said second shaft, said change-over frame being swingable together with said supporting member to move along the direction of the axes of said sprockets around said first shaft with respect to said fixing member and carrying first and second pulleys for guiding a driving chain, said first pulley being supported rotatably to the foremost end of said change-over frame through a third horizontal shaft in parallel with said second shaft.