A bicycle electric rear derailleur 26 comprises a base member 41, a movable member 43, and a linkage structure 45. The linkage structure 45 is configured to operatively couple the base member 41 to the movable member 43. The linkage structure 45 includes at least one of a wireless communication unit receiving space S11, a charging-portion receiving space S12, a control-board receiving space S13, an operating-member receiving space S14, a display-unit receiving space S15, a connector receiving space S16 and a data-reader receiving space S17.