A head drum assembly comprises a plurality of vent holes formed through an upper drum to allow an air under the upper drum to communicate with an air above the upper drum, a flange member for making an air flow within a space between the upper drum and a lower drum, in response to a rotational movement of the upper drum, in such a manner that air is introduced through the vent holes and is radially outwardly flown away from the space, and a plurality of outlet ports for guiding the flown air to apply the flown air against a magnetic tape retained around the head drum assembly.
