A command device for a bicycle gear change, comprising: a rotating drum (2) provided with a rotation axis (x) and being predisposed to rotate in opposite directions in order to wind at least a portion of a change-activating cable (3) on a lateral surface of the rotating drum (2); means for rotating, predisposed on command to rotate the rotating drum (2) in opposite directions according to predetermined angular steps; means for retaining predisposed to hold the rotating drum (2) in a position in absence of commands made to the means for rotating. The rotation axis (x) of the rotating drum (2) is perpendicular with respect to an advancement direction of the bicycle, that is, parallel to the rotation axis of the front wheel of the bicycle.