PURPOSE: To improve the conversion efficiency by extending the range of character strings, which can be taken as the rule conversion object of one rule, to reduce the memory capacity of a rule dictionary with respect to KANA (Japanese syllabary)-KANJI (Chines-e character) conversion using the rule dictionary.

CONSTITUTION: A KANA reading character string is inputted from an input device, and a KANA-KANJI conversion program refers to a fundamental dictionary where expressions of reading of words are stored, a part-of-speech information part, and a connection table to subject the inputted KANA reading character string to KANA-KANJI conversion. A rule retrieval program refers to the rule dictionary where rules having patterns of word strings in the fundamental dictionary and their rewrite information are stored, to retrieve the rule coinciding with the conversion result. If rule reconversion is indicated at this time, the designated reading character string is subjected to KANA-KANJI conversion again. Coincidence between the part of speech of the conversion result and the designated part of speech indicates that the rule coinciding with the conversion result has been retrieved, and a rule rewrite program rewrites contents of the pertinent KANA-KANJI conversion result based on the rule dictionary.