PURPOSE:To sharply save an idle area information label area by saving an idle area information label to a saving device, updating data only in the saving device at the time of forming a new file to be frequently generated or expanding an already existing file, and only at the time of ejecting a rewriting disabled medium from a file device, writing data in the rewriting disable medium. CONSTITUTION:Only when it is necessary to form a new file or expand an already existing file in the rewriting disable medium 2, an idle area information label updating means 1-2 inputs a saved label 3-1 from the saving device 3, updates the contents of the label 3-1 and newly writes the updated contents as a saved label 3-1. When the ejection of the medium 2 is requested, an idle area information label restoring means 1-3 inputs the saved label 3-1 from the device 3 only when the label 3-1 is updated, writes a new idle area information label L4 in the medium and ends the writing to eject the medium 2.
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