To make it possible to input Roman characters by a sense close to a full keyboard even in an environment limiting the number of keys by inputting all characters, voiced sound marks and p-sound marks in HIRAGANA (cursive form of Japanese syllabary) by seven consonant keys and five vowel keys.

HIRAGANA characters 'ka, ki, ku, ke, ko' are inputted by combining a 'K' key and 'a', 'i', 'u', 'e', 'o' keys, HIRAGANA characters 'sa, shi, su, se, so' are inputted by combining an 'S' key and the 'a', 'i', 'u', 'e', 'o' keys, HIRAGANA characters 'ta, chi, tsu, te, to' are inputted by combining a 'T' key and the 'a', 'i', 'u', 'e', 'o' keys, and HIRAGANA characters 'na, ni, nu, ne, no' are inputted by combining an 'N' key and the 'a', 'i', 'u', 'e', 'o' keys. Similarly HIRAGANA characters 'ha, hi, fu, he, ho', 'ma, mi, mu, me, mo' and 'ra, ri, ru, re, ro' are respectively inputted by combining an 'H' key and the 'a', 'i', 'u', 'e', 'o' keys, an 'M' key and the 'a', 'i', 'u', 'e', 'o' keys and an 'R' key and the 'a', 'i', 'u', 'e', 'o' keys. Voiced sound marks are inputted without using 'D', 'Z', 'G', 'J', and 'V' keys and p-sound marks are inputted without using a 'P' key.