A data managing system comprising a storage medium adapted to store data in record units, a record comprising a plurality of fields, an update device adapted to update data that is stored on the storage medium by carrying out reading and writing of desired data on the storage medium, and an update file input device adapted to receive the input of an update file that contains a stored field specifying structure that specifies a field that is to be updated in the record and that contains the updated data for the field that is to be updated; wherein the update device is adapted to write, for the record, the updated data that has been extracted from the update file into a field that has been specified by the stored field specifying structure of the update file, characterized in that the update file contains, as the stored field specifying structure, a stored data flag that indicates the presence or absence of updated data for each of the plurality of fields in the record, and contains an updated data flag that indicates whether to update or not for each of the plurality of fields in the record and disposes the updated data in the disposition sequence of the plurality of fields in the record; and in that the update device is configured to perform the following steps: when the updated data flag indicates that updating is to be carried out, then the update device determines the presence or absence of updated data by using the stored data flag; and when the updated data flag indicates that updating is to be carried out and the stored data flag indicates that the updated data is not present, the update device is adapted to erase the data of this field, when the updated data flag indicates that updating is not to be carried out, the update device is adapted to maintain the data of this field, and when the updated data flag indicates that updating is to be carried out and the stored data flag indicates that the updated data is present, the update device is adapted to successively extract the updated data from the update file in the disposition sequence of the corresponding updated data, and successively write the corresponding extracted updated data into a field for which the stored data flag indicates the presence of updated data in the disposition sequence of the plurality of fields in the record. when the updated data flag indicates that updating is to be carried out, then the update device determines the presence or absence of updated data by using the stored data flag; and when the updated data flag indicates that updating is to be carried out and the stored data flag indicates that the updated data is not present, the update device is adapted to erase the data of this field, when the updated data flag indicates that updating is not to be carried out, the update device is adapted to maintain the data of this field, and when the updated data flag indicates that updating is to be carried out and the stored data flag indicates that the updated data is present, the update device is adapted to successively extract the updated data from the update file in the disposition sequence of the corresponding updated data, and successively write the corresponding extracted updated data into a field for which the stored data flag indicates the presence of updated data in the disposition sequence of the plurality of fields in the record.