To preclude displaying unnecessary conversion candidates caused by a wrong confirming operation and improve usability in a determinative history-controlling operation which controls the order in displaying the conversion candidates based on the determinative history.

When kana-to-kanji conversion is made by a Japanese language word processor, an operation executed immediately after the kana-and-kanji conversion is made is monitored. Then, the operation executed immediately after the kana-to-kanji conversion is decided that a user has wrongly determined the character string when there is a deletion of a character string from what has been determined just before the operation, and deletes the history of the confirmed character string from the determinative history. In the file processing of a personal computer, when the conversion of a format and saving of a file are made, the user is judged to wrongly determine the saving and place where data and stored, and the format and place where the data are stored relating to the file deleted are deleted from the determinative history.