PURPOSE: To prepare a proper document by informing a document preparator that a KANA (Japanese syllabary)/KANJI (Chinese character) character string is a colloquial expression.

CONSTITUTION: A KANA/KANJI conversion part 24 converts an input reading string 21 into a KANA/KANJI character string while referring to a word dictionary 22 and an adjunct dictionary 23. Attributes indicating colloquial expressions are registered in the dictionaries 22, 23. If a colloquial expression is included in the converted KANA/KANJI character string, a clause including the colloquial expression is displayed by a format to be discriminated from a part including no colloquial expression. When original expressions are stored in the dictionaries 22, 23 in addition to the attributes, processing for substituting an original expression for a colloquial expression can also be executed.