Abstract: In order to improve a gear change system for bicycle derailleur gears, comprising a first chain changer for shifting the chain to different chain wheels on the pedal-crank side, a second chain changer for shifting the chain to different pinions on the wheel side, and a gear change device with a first switching unit for the first chain changer and with a second switching unit for the second chain changer and with a manually operated switching element by means of which both switching units can simultaneously be actuated so that by means of the latter the chain can simply be shifted to chain wheel/pinion combinations selected for a gear sequence and from a switched gear a transition is possible only to the next closest gear in the gear sequence, in such a way that a great degree of ease and comfort in switching can be achieved with the least possible effort, it is proposed that the first chain changer is a mechanical chain changer mechanically controllable through the first switching unit, and that the second ch