A data management system that facilitates table merges without the necessity of knowledge about a database or creating an environment therefore is provided. With a processor unit, a merging sheet (merged table) for merging a plurality of spreadsheets (tables) is recorded, and then stored in an external storage device. A table designated by the user through mouse operation and the merged table are compared; if cells of the same data exist in a specific column, the data in rows to which said cells in the table belong are merged to rows to which relevant cells of the merged table belong; for rows to which cells existing only in the table belong, they are added as new row data to the merged table. Furthermore, a flag for identifying each table is recorded in rows merged or added to the merged table.