<p>A head drum assembly and method of manufacturing a magnetic recording/reproducing apparatus are disclosed. In the assembly, for application of a pre-load on the upper and the lower bearings, the upper and the lower bearings are installed in a loosely fitting manner on the shaft. An elastic member for applying a load on an inner ring of either of the upper and the lower bearings is provided so that simplification of the manufacturing process of the head drum assembly, cost reduction, and productivity improvement are achieved.</p>