4. The method of claim 1 , further comprising retrieving a word which includes the target character string in part from a set of words registered in a dictionary; and wherein the converted character string is generated by appending at least one character, which is located in at least either one of the previous and subsequent positions of the target character string in the retrieved word, to the target character string.
5. The method of claim 4 , wherein the converted character string is generated by appending at least one character, which is common to a predetermined reference number or more of words among a plurality of words partially including the target character string in the dictionary, to the target character string.