A radial bed catalytic conversion unit having an outer cylindrical chamber (1), an inner chamber (2) which is also cylindrical, the annular zone included between the outer chamber and the inner chamber, termed the reaction zone (I), is filled with catalyst under slow gravitational flow, and the feed is introduced via an inlet pipe (E), connected to an intermediate box (F) which is in turn connected to a plurality of distribution tubes (3) disposed inside the reaction zone (I) in the vicinity of the outer chamber (1).