The Empire of Japan, until AD 1889, the 21rst year of the Meiji era, had never had a Constitution. The Tokugawa Bakufu, the feudal government of the Shogun, had a totally different conception of law and justice, based on confucian thought and buddhist paternalism. The Meiji Restoration brought about a deep change, firts of all by achieving a rapid modernization of the national industry, and by the adoption of legal and juridical categories as imported by the West. Hence, a coherent theorization of a constitutional framework, based on the Prussian Constitution, was a fundamental step in the construction of the Meiji constitutional State. Thus, the origin of Japanese Constitutionalism is to be found not just in the adoption of the Meiji Charter, but first in the prior importation of western juridical categories, as a legal forma mentis which was seen by the Meiji oligarchs as essential in building a modern State.