A device for unloading and placing rails in a track parallel to another existing track, which is assembled in the rear of the rail carrier train (Tc), which runs on the existing main track (Vd), coupled in a series of auxiliary wagons (V1, V2, V3), and formed by a series of metal structures (P1, ..., P9) fixed in said auxiliary wagons added in the rear of the rail carrier train, which determine several fixed guiding points longitudinally distributed in a suitable manner along these auxiliary wagons, both in the transverse and in the vertical direction, in a smooth transition and according to the standards in relation to the radii and buckling of the rail, from its transport position on the rail carrier (Tc) to its definitive position on the bearing plate of the crossties previously positioned in an also definitive place on the subgrade of the parallel track (Vp).