A device for generating a flat, laminar gas jet, in particular suitable for hot coating processes for metal strips, comprising - a longitudinal delivery manifold having a peripheral wall, the peripheral wall being provided with first holes, - a levelling pre-chamber communicating with said longitudinal delivery manifold through said first holes, - a levelling pipe communicating at a first end thereof with said levelling pre-chamber, - a nozzle adapted to generate the flat gas jet, - said levelling pipe communicating at a second end thereof with said nozzle, said second end being opposite to and having a smaller section than the first end, so as to be tapered and to create a gas flow path from said levelling pre-chamber to the nozzle, said path defining a curved medial development surface, - at least a first holed partition and a second holed partition arranged in said levelling pipe and perpendicular to said curved medial development surface, thereby defining at least two successive, adjacent portions (3a, 3b) of the levelling pipe which are connected to each other, the second holed partition being arranged downstream of said first partition, wherein the first holes are provided only in a first longitudinal sector of the peripheral wall of the delivery manifold and said levelling pre-chamber extends externally at least about said first longitudinal sector, wherein a first portion of the levelling pipe is externally wound around a second longitudinal sector of the peripheral wall of the delivery manifold, adjacent to the first longitudinal sector, the second longitudinal sector having an angular extent in the range from 30° to 180°, said curved medial development surface is represented by an ideal continuous curved surface without any angular points, wherein a second portion of the levelling pipe is arranged in a substantially tangential direction with respect to the delivery manifold, downstream of said second longitudinal sector, wherein the section of said levelling pipe in a stretch between the first partition and an outlet pipe decreases to about 1⁄4 of an initial value, and wherein said first holed partition comprises second holes and said second holed partition comprises third holes and wherein the diameters (Φ1, Φ2, Φ3) of the holes (12, 25, 26) decrease along the gas flow path as the number of holes (12, 25, 26) increases. - a longitudinal delivery manifold having a peripheral wall, the peripheral wall being provided with first holes, - a levelling pre-chamber communicating with said longitudinal delivery manifold through said first holes, - a levelling pipe communicating at a first end thereof with said levelling pre-chamber, - a nozzle adapted to generate the flat gas jet, - said levelling pipe communicating at a second end thereof with said nozzle, said second end being opposite to and having a smaller section than the first end, so as to be tapered and to create a gas flow path from said levelling pre-chamber to the nozzle, said path defining a curved medial development surface, - at least a first holed partition and a second holed partition arranged in said levelling pipe and perpendicular to said curved medial development surface, thereby defining at least two successive, adjacent portions (3a, 3b) of the levelling pipe which are connected to each other, the second holed partition being arranged downstream of said first partition,