A file format converting method for converting a first format file in a first file system of a storage apparatus to a second format file in a second file system is provided. The method includes creating a temporary file and defining a data amount of the temporary file as a first predetermined value; defining a start position of the temporary file to be the same as that of the first format file; and defining the data amount of the temporary file to be the same as that of the first format file to generate the second format file.