‘March 11 East Japan Great Earthquake’ is being summarized as an unheard-of ‘Mega-complex Chain Disasters‘ combined with mega-tsunami caused by a mega -quake and its resultant Fukushima nuclear accident. Particularly, the Fukushima nuclear accident is understood as taking on the character of a man-made disaster other than a natural disaster. The Center for Japanese Studies of Korea University has accumulated lots of products by ‘Post 311 and Human Disaster (Calamity) and Safety & East Asia Research Team.’ It’s thought that the background of such products might be attributable to the establishment of common awareness that ‘Disaster’ and ‘Safety’ are not limited to a problem of a certain country only now. ‘The ‘Disaster’-caused extraordinary damage besides contingencies shakes the foundation of a nation, and the victim country comes to struggle for relieving the shock beyond the times, and also comes to devote itself to minimizing the damage. Such a series of efforts might not be limited to modern times. Based on the above short views, this study tried to analyze how the ‘Natural Disaster and Unexpected Change’, which occurred intensively during the period of the Japanese Ritsuryo Court after the 7th century, worked on the transformation of the Japanese Ritsuryo Court. As a result, this study could confirm that the ‘Deikan Earthquake’ whose size is said to be almost the same as ‘311 East Japan Great Earthquake’ also had an immense influence on the transformation of the Japanese Ritsuryo Court after the mid-9th century. In short, Japan after the mid-9th century came to give up the 4 major values, such as ‘Improvement of Ritsuryo Court’, ‘Compilation of National History’, ‘Construction of Capital sites’, and ‘External Views aiming at little Empires of Dongie (tribes of China’s northeastern region).’ It might be hard to deny that fact that there existed ‘Natural Disaster & Unexpected Change’ occurring frequently after the mid-9th century in the background of the change and swift of the national policy.