Device for actuating a front derailleur of a bicycle to displace a transmission chain between a first toothed wheel and a second toothed wheel , the second toothed wheel having a diameter smaller than the diameter of the first toothed wheel , the device comprising: an indexer operatively active on the front derailleur and comprising a first lower stop position (P1), and a third lower stop position (P3) at which the transmission chain is engaged on the second toothed wheel , and wherein the first lower stop position (P1) corresponds to a position of the derailleur substantially adjacent to a lower end stop of the derailleur, the third lower stop position (P3) corresponds to a position of the derailleur further from the lower end stop ; said indexer comprising a first upper stop position (P4) corresponding to an engagement of the transmission chain on the first toothed wheel and characterized by the indexer comprising a second lower stop position (P2), wherein the second lower stop position (P2) is configured to center the front derailleur on the second toothed wheel , the second lower stop position (P2) is arranged between the first lower stop position (P1) and the third lower stop position (P3), and the second lower stop position (P2) corresponds to an intermediate position of the derailleur between the first (P1) and the third (P3) lower stop position, and at least one control lever operatively active on said indexer to switch the latter between the first lower stop position (P1), the second lower stop position (P2) and the first upper stop position (P4), wherein with a single actuation of the control lever the indexer is switched from the first upper stop position (P4) to the second lower stop position (P2). an indexer operatively active on the front derailleur and comprising a first lower stop position (P1), and a third lower stop position (P3) at which the transmission chain is engaged on the second toothed wheel , and wherein the first lower stop position (P1) corresponds to a position of the derailleur substantially adjacent to a lower end stop of the derailleur, the third lower stop position (P3) corresponds to a position of the derailleur further from the lower end stop ; said indexer comprising a first upper stop position (P4) corresponding to an engagement of the transmission chain on the first toothed wheel and characterized by the indexer comprising a second lower stop position (P2), wherein the second lower stop position (P2) is configured to center the front derailleur on the second toothed wheel , the second lower stop position (P2) is arranged between the first lower stop position (P1) and the third lower stop position (P3), and the second lower stop position (P2) corresponds to an intermediate position of the derailleur between the first (P1) and the third (P3) lower stop position, and at least one control lever operatively active on said indexer to switch the latter between the first lower stop position (P1), the second lower stop position (P2) and the first upper stop position (P4), wherein with a single actuation of the control lever the indexer is switched from the first upper stop position (P4) to the second lower stop position (P2). <EOS>