Discovery of the Tiansheng Statutes has made an epoch for research aimed at reconstructing the Tang statutes. The author tells what former comparative studies of the statutes of ancient Japan and Tang made clear in Japan, so that it will be useful for scholars studying the Tang history in China. The research of the rituryô system was begun to make by the pupils of Sakamoto Taro at the University of Tokyo after the World War II. The most excellent results were obtained by the analysis on the taxation system by Aoki Kazuo and the following analysis on the statutes of households (Ko-ryô) and arable fields (Den-ryô) by Yoshida Takashi. Yoshida thereafter, accepting the suggestions of Ishimoda Sho and Inoue Mitusada, published a comprehensive study of the rituryô state from the viewpoint that the Rituryô law came to make the early society of Japan civilized in the ancient East-Asia. In regard to the bureaucracy of ancient Japan, Seki Akira and Hayakawa Shohachi laid emphasis on the aristocratic elements of the rituryô state and pointed out the importance of oral directives in comparison with the situation in Tang. In recent years research was made on introducing the system of rites especially into the Heian Japan, and Osumi Kiyoharu pointed out that the rites in the 8th century were inherited from the former regime of the Yamato state.