Abstract: A heat exchanger (10) for indirectly heating, drying and cooling materials comprises a hollow rotor (40) having an inlet (46) of heating and cooling medium and an outlet (47) of the medium or its condensate, a casing mounted on the hollow rotor, a plurality of disc-shaped base boards (20), a plurality of annular ducts (21, 23; 22, 24) projected from both side surfaces (11, 12) of the base boards (20), the duct forming a passage communicating with the inlet (46) and the outlet (47), arranged so as to be partly superposed sequentially on both front and back surfaces (11, 12) of the base board (20) from the inner peripheral edges to the outer peripheral edges of the base boards (20) in such a manner that partition plates for shielding the ducts (21, 23; 22, 24) being provided in the superposed positions.