In the manufacture of a casing base for a hard disc drive device, an elongate semi-product of a light metal having a predetermined sectional profile having opposite side frame portions, is extrusion molded and then cut to a predetermined length to obtain an eventual casing base, which is then formed with necessary holes and recessed or raised portions using a press, thus completing the casing base. Like the case of die casting, no cavities are generated, so that it is possible to readily carry out washing and surface treatment. In addition, unlike the case of forming frames in a sole press process, a large number of press forming steps are not involved, and it is possible to permit mass production of a highly accurate and highly rigid product in a small number of steps and at a low cost of manufacture.