To internationalize Japanese words accordant with the world standard US ASCII codes and also to turn KANA (Japanese syllabary) into the Japanese words via the modification of the KANA by using the codes listed in a specific table as the Japanese word phonetic characters and accordingly expressing the Japanese words in an easy-to-read way.

The codes which are listed in the 1st to 3rd tables are used as the Japanese word phonetic characters. That is, 'X' which is not hitherto included in the Roman letters is used as a voiceless identifier, and the original form of an independent vowel is expressed in two characters. Then the identifier 'X' can also be used for separating the characters as necessary in addition to an X code of a 2nd table. The X code is used with the conventional Roman letters. As a result, the Roman characters are abundant with variations and the number of letters can be decreased by 5 to 20% to be read more easily although the conventional Roman letters have high occurrence frequency of vowels and are short of variations to be hard to read. Furthermore, the single vowels are mixed into the Roman letters and accordingly similar to the international character sounds to obtain the internationally familiar characters.