12. The Hangeul input method of claim 11 , wherein the basic consonants assigned to the selected consonant key are sequentially and circularly selected by repeatedly operating the selected consonant key, the basic vowels assigned to the selected vowel key are sequentially and circularly selected by repeatedly operating the selected consonant key, and the extended consonants to be converted from the corresponding basic convertible consonants are sequentially and circularly selected by repeatedly operating the shift key.
12. The Hangeul input method of claim 11 , wherein the basic consonants assigned to the selected consonant key are sequentially and circularly selected by repeatedly operating the selected consonant key, the basic vowels assigned to the selected vowel key are sequentially and circularly selected by repeatedly operating the selected consonant key, and the extended consonants to be converted from the corresponding basic convertible consonants are sequentially and circularly selected by repeatedly operating the shift key. 13. The Hangeul input method of claim 12 , wherein the extended consonants are circularly selected in the sequence of an aspirate of the corresponding basic convertible consonant and fortis of the corresponding basic convertible consonant by repeatedly operating the shift key.