"Waga Yado" is an idiom which stands for "my residence" in Japanese language. This idiom creates a problem in the history of Japanese dwelling house because when this idiom was evolved. The word "Yado" meant etymologically not a "house" i.e."Ya" but an "outer-space" i.e."To" or even an "openning" i.e. "To" of a building ("Ya") in ancient Japan. To determine precisely the age, and the process through which this idiom was evolved, the author researched this word thoroughly in the four areas of literature completed in the 8th century ("Kojiki", "Nippon Shoki", "Fudoki", and "Manyoshu"). He discovered about 120 words in "Manyoshu", an anthology of about 4, 500 poems of ancient Japan, and determined the following points. 1. The first poem which has "Waga Yado" was composed in the reign of Emperor Tenchi (662-671 A. D.), though this "Waga Yado" did not mean "my residence" at the time. 2. In several poems composed in 730 A. D., we clearly find that the idiom had been incorporated into the language. 3. Upon comparing these instances with other "Waga Yado" before 730 A. D., the author found that the first "Waga Yado" which stands for "my residence" occurred in the poem by Prince Fozumi composed in the beginning of the 8th century. At the same time, the author found that the 8th century poems which have "Waga Yado" in "Manyoshu" always speak of plants in a garden such as "Hagi (bush clover)", "Tachibana (orange)", "Ume (plum)", "Nadeshiko (wild pink)", etc., or the Moon, Birds, Wind and the like. So we can say that the expression "Yado" i.e. "residence" is always found up in those poems with the "petit and intimate beauties of Nature". On the other hand, one of the most traditional characteristics of the history of Japanese dwelling house was that the dwelling house always had a garden in which the householderes could live with and enjoy "petit and intimate Nature". This carried throughout history untill the 19th century. Another problem in the history is when this tradition actually began. In conclusion, it is the opinion of the author that the evolution or the invention of the idiom "Waga Yado" coincides with the formation of this "Nature" tradition in the history of the Japanese dwelling house.