This book is based on establishment, development and decline of Great Gaya(大伽倻) in Koryŏng(高靈). Great Gaya(大伽倻) was a country down the line of Koryŏng-kun(高靈郡) in Kyŏngsangbuk-to(慶尙北道) for 520 years, from 42 to 562. However, even political system has not been agreed in academia because the understanding of history of this country is not accomplished despite of the long period. The author investigates process of formation and internal systems of Great Gaya(大伽倻) based on existing researches and materials represented so far.