Unit for winding and unwinding cables of a cable-laying apparatus, comprising a reel to support the cables to be wound or unwound, a support frame configured to keep said reel in a raised position with respect to the ground, and a rotation shaft solid with the reel and associated with a corresponding hydraulic drive unit; the unit also comprises at least a dynamic braking device associated with the rotation shaft and configured to allow, according to a first operating mode, the normal rotation of the shaft and therefore of the reel for winding or unwinding the cables, and to exert on the shaft and therefore on the reel, according to another operating mode, a dynamic braking condition that allows the shaft to rotate in a braked configuration for at least a certain period of time and prevents the instantaneous stoppage of the rotation of the reel.