The invention relates to a device which comprises a gear change fork (1), a hydraulic cylinder including a stationary cylindrical spindle (2) with a stationary transverse wall (3) projecting from said spindle (2) and a piston that is translatably movable by sliding over said transverse stationary wall (3). The piston consists of a piston body (4) closed by a radial closing part referred to as a “plug” (5) so as to define two inner chambers (6, 7) of the cylinder, which are situated on either side of said stationary transverse wall (3), respectively. Means for pressurizing both of the two cylinder chambers (6, 7) are provided for moving the movable piston (4, 5) in one direction or another. In the device according to the invention, the piston body (4) is directly built into the gear shift fork (1) whereby, as a result of the pressure in a cylinder chamber (6, 7), it is the fork (1) that moves translatably.