PURPOSE: To simplify processing in an editing part and an inverse converting part by providing an input character string buffer to make a roman character string correspondent to HIRAGANA (cursive form of Japanese syllabary), to which roman/HIRAGANA conversion is executed.

CONSTITUTION: An input character string buffer 12 makes the plural roman characters to each character as the result of the roman/HIRAGANA conversion in a roman/HIRAGANA conversion part 11, and stores the characters. For example, the input of 'KYOUHA' is converted to 'kyouha (HIRAGANA)' and 'K' is made correspondent to 'ki (HIRAGANA)', 'YO' is made correspond ent to 'you (HIRAGANA)', 'U' is made correspondent to 'u(HIRAGANA)' and 'HA' is made correspondent to 'ha (HIRAGANA). As a result, when the 'yo (HIRAGANA)' is deleted, the 'YO' is deleted from the input character string buffer 12 and an inverse conversion request is received, the 'YO' can be returned to the input characters of 'KUHA'. Then, the processing can be simplified in an editing part 13 and an inverse converting part 14.