A conversion method for converting a format of a plurality of pieces of data included in a file, the conversion method that causes a computer to execute a process comprising: generating another file that includes a plurality of pieces of format converted data associated with the plurality of pieces of data included in the file by applying an algorithm to the plurality of pieces of data, a process of the algorithm including: associating, when identification information of pre-format-conversion data is associated with data in the plurality of pieces of data, the identification information with format converted data corresponding to the data; and associating, when the identification information is not associated, newly generated identification information with the format converted data; characterized by determining, by referring to relationship information between the identification information associated with each of a plurality of pieces of data included in the another file and a position of each of the plurality of pieces of data in the another file, whether one of a plurality of pieces of identification information is associated with a plurality of positions in the another file; and changing, when one of the plurality of pieces of identification information is associated with the plurality of positions in the another file, the identification information associated with one of a plurality of pieces of data at the plurality of positions from among the plurality of pieces of data included in the another file. generating another file that includes a plurality of pieces of format converted data associated with the plurality of pieces of data included in the file by applying an algorithm to the plurality of pieces of data, a process of the algorithm including: associating, when identification information of pre-format-conversion data is associated with data in the plurality of pieces of data, the identification information with format converted data corresponding to the data; and associating, when the identification information is not associated, newly generated identification information with the format converted data; associating, when identification information of pre-format-conversion data is associated with data in the plurality of pieces of data, the identification information with format converted data corresponding to the data; and associating, when the identification information is not associated, newly generated identification information with the format converted data; characterized by determining, by referring to relationship information between the identification information associated with each of a plurality of pieces of data included in the another file and a position of each of the plurality of pieces of data in the another file, whether one of a plurality of pieces of identification information is associated with a plurality of positions in the another file; and changing, when one of the plurality of pieces of identification information is associated with the plurality of positions in the another file, the identification information associated with one of a plurality of pieces of data at the plurality of positions from among the plurality of pieces of data included in the another file. <EOS>