Abstract: Gear shifting device for a cycle having a chain and pinion transmission is provided, which includes a mobile gear shift assembly adapted to laterally displace the chain for enabling passage from one gear to another gear; transformation elements for transforming rotation of at least one pivoting gear into a lateral displacement of the mobile gear shift assembly; and a control mechanism for controlling lateral displacement of the mobile gear shift assembly. Further, the gear shifting device can include an indexing mechanism to further ensure exact positioning of the gears.