strength of the thin film layer is improved thus thin film layers excellent in durability and running characteristics are produced although the embodiment illustrated in fig1 illustrates the case where two cylindrical cans are provided to divide the support conveyance path onto three sections it is a matter of course that the invention is not limited to the specific embodiment and that a larger number of cylindrical cans may be provided to form multilayered thin film layers although the aforementioned embodiment has been described with respect to the case where sputtering is used for film preparation it is to be understood that the invention is not limited thereto in particular the invention is applicable to the case where evaporation as shown in fig4 is used and both film preparation sources 21 and 22 are arranged below the cylindrical cans 1 and 2 to prepare films on the upper and lower surfaces of the support 10 any suitable method such as ion plating cvd and the like can be used as described above according to the present invention to ensure that the cylindrical cans contact the support in a suitable manner for cooling the support the tension of the support is adjusted to satisfy expressions 1 and 2 further thin film layers of a magnetic metal are.