An apparatus for achieving the return of a chain to a rear derailleur tension pulley more easily by means of pedaling action when the chain falls off from the tension pulley is provided. The rear derailleur is equipped with a base component, a link mechanism, a movable component, Outer Plate 20, Inner Plate 21, Guide Pulley 22, Tension Pulley 23, and Chain Return Section 32. The base component is a component which is mounted on the frame. The link mechanism is a mechanism of which one end is mounted on the base component. The movable component is a component which is mounted on the other end of the link mechanism, and which can be relatively displaced from the base component. The outer plate is a component which is mounted on the movable component so as to undulate like a see-saw. The inner plate is a component which is installed so as to face the outer plate. The guide pulley is a pulley which is mounted onto a portion on one edge of the plates, between the plates, so as to freely rotate and move in the axial direction, and which can be engaged with the chain. The tension pulley is a pulley which can be engaged with the chain, and is mounted onto a portion on the other edge of the plates, between the plates, so as to freely rotate. The chain return section is installed at a position on the inner plate which is proximal to the position at which the tension pulley is mounted, in a manner so that the clearance from the chain at this position is narrower as compared to the clearance at other positions.