The Ikaruga School is one of the schools of flower arrangement, "Ike-bana" and tea ceremony, "Cha-no-yu" in Japan. This School is connected with Horyuji Temple which is the headquarters of the Shotoku sect of Buddhism. The Temple consists of two groups of buildings, that is to say, the Sai-in (West group) and the To-in (East group). It is generally believed that the Sai-in which was called Ikaruga-Dera originally was established in the Asuka Period (in 607 A.D.) by the Crown Prince Shotoku-Taishi. "Ikaruga" is the name of the district, where the Temple stands. In this paper, I try to investigate the structure and form of the "Iemoto" System analyzing the Ikaruga School and many other schools. I think the "Iemoto" System may be divided into two parts, namely, the varied and multiform relationships into which men necessarily enter in the course of arranging flowers or tea ceremony, and the norms or standards governing behavior. This study serves to focus our attention upon a way of life, a group, and a social organization or social structure in Japan. The Japanese flower arrangement had its primitive beginnings in the age when Buddhism was imported into Japan from China. Since then, Buddhism has contributed a great deal to enhance Japanese culture, not only in the field of religion but also of Japanese art, for example, architecture, sculpture, and so on. It was one of the customs of Japanese to place flowers as a offering to Buddha in the temple. Therefore the purpose of flower arrangement was originally to decorate the Buddhist altar with flowers. Of many arts peculiar to Japan, flower arrangement and tea ceremony are especially familiar to us In daily life. A knowledge of flower arrangement is considered so important to women that even busy peoples take the time to practice arranging flowers after their business hours. Tea ceremony today is practiced by women and men, and especially by young girls. The present head master of the Ikaruga School is Kyoichi Saeki. Exhibitions of flower arrangement put on by this School are held on festival days of Horyuji Temple. A set of traditional rules is maintained by the members of this School in arranging flowers. Though this School is supported by Horyuji Temple, it is important for us to notice the mutual aid between this Temple and the Ikaruga School.