A combined washing and rinsing device for a dishwashing machine, in particular for a professional dishwashing machine, comprising a single arm delimited on the outside by a first face equipped with a plurality of first, washing, nozzles, and with a plurality of second, rinsing, nozzles, which are arranged at least partly aligned with each other, the first nozzles to form at least a first row in a longitudinal direction of extension of the arm and the second nozzles to form at least a second row in said longitudinal direction; a hub carried by a second face of the arm opposite to the first, and arranged substantially on the center-line of the arm, which is, in use, rotating on the hub, about a symmetry axis of the hub; and a double hydraulic delivery circuit defined by the arm for separately supplying the first and the second nozzles; wherein: i) - the arm consists of an internally hollow body formed by a first and by a second half shell coupled to overlap each over at the part of the respective concavities (20, 21) thereof, the first half shell delimiting, on the part opposite to the concavity thereof, the first face and the second half shell delimiting, on the part opposite to the concavity thereof, the second face; ii) - the double hydraulic delivery circuit is obtained inside the second half shell by means of a longitudinal rib which overhangs inside the concavity of the second half shell and which couples in a fluid sealing manner with the first half shell to form, inside the arm, a first and a second chamber, which are separate from each other, into which the first and the second nozzles, respectively, are lead; iii) - the first and second half shell (18, 19) are integrally fastened to each other in a fluid sealing manner; and wherein the hub is obtained only and completely integral in one piece with the second half shell and is formed by a first and a second sleeve, which are arranged coaxial and having, at the part of the second face, an axial extension which is different with respect to each other; characterized in that the first sleeve is arranged radially on the outside of the second sleeve and integrally supports the second sleeve by means of at least one pair of diametrically opposite spokes, which delimit, between the first and the second sleeve (29, 30), in the second half shell, a pair of circumferentially extending axial through apertures, for access to the first chamber. i) - the arm consists of an internally hollow body formed by a first and by a second half shell coupled to overlap each over at the part of the respective concavities (20, 21) thereof, the first half shell delimiting, on the part opposite to the concavity thereof, the first face and the second half shell delimiting, on the part opposite to the concavity thereof, the second face; ii) - the double hydraulic delivery circuit is obtained inside the second half shell by means of a longitudinal rib which overhangs inside the concavity of the second half shell and which couples in a fluid sealing manner with the first half shell to form, inside the arm, a first and a second chamber, which are separate from each other, into which the first and the second nozzles, respectively, are lead; iii) - the first and second half shell (18, 19) are integrally fastened to each other in a fluid sealing manner; and wherein the hub is obtained only and completely integral in one piece with the second half shell and is formed by a first and a second sleeve, which are arranged coaxial and having, at the part of the second face, an axial extension which is different with respect to each other; characterized in that