To save the trouble to convert a character to an additional character and to improve its operability.
To convert a character 'ken' in KANJI(Chinese character) included an illustrated word 'kentou' to an additional character (1) in KANJI, an operator inputs the reading of the object character 'tou' before conversion. Then the JIS KANJI code of this object character 'ken' is specified and the character is converted to the character (1) according to the character code. The character (1) is an additional character as a variation of the character 'ken' and the outline data of the character (1) is made to correspond to the same character code with the JIS KANJI code of the character 'ken'; when additional character conversion is performed, the outline data is employed as the character (1) while the character code of the character 'ken' is left as it is.