Bicycle rear derailleur device (1) comprising a chain guide assembly (15) made up of two parts: a guiding cage (28) and a tension cage (32). It also comprises a movable member (18) coupled to a base member (10) via a linking member (13) to align the chain guide assembly (15) with the different sprockets. Said tension cage (32) carries a tension pulley (11), is pivotably coupled to the movable member (18) and is biased by a main spring or biasing member (17). The guiding cage (28) carrying a guiding pulley (14), and the tension cage (32) are both configured to move either jointly or independently of each other, such the distance between both pulleys (14, 11) is fixed or free respectively, varying as a consequence the chain tension. To do so, the guiding cage (28) is pivotally coupled to the tension cage (32) comprising between them coupling means (16) that selectively and reversibly make both cages united or not.