The invention relates to an air diffuser device (1) for ventilating rooms and to be installed in a ventilation duct opening in a wall or ceiling of a room, said air diffuser device (1) comprising a baffle element (10) having a central region (10a) and a peripheral region (10b) with a peripheral edge (12; 13) for deviating at least a part of a ventilation air flow entering said room through said ventilation duct opening in a flow direction with an air flow component parallel to said wall or ceiling. The baffle element (10) comprises a plurality of slits or grooves (11) each extending from the central region (10a) of said baffle element (10) to the peripheral region (10b) of said baffle element (10). In addition, the peripheral edge (13) of said baffle element (10) has a plurality of radially extending indentations (14) spaced from each other along the periphery of said baffle element (10).