《還城楽》とは、その由来が複数ある現行の舞楽であり、現行諸舞楽のなかでも、特殊な構造を持つ演目のうちの一つとなっている。本論文は、こうした舞楽《還城楽》の起源と舞踊構造のなかに横たわる複相性を明らかにすることを目的とする。
　起源と舞踊構造の調査研究は、以下の2つの方法によった。起源研究は、中国と日本の古文献により、舞踊構造研究は、漢字とカタカナで書かれたいわゆる『明治撰定譜』の譜字を分析することに拠った。
　まず、起源については、演目内に小道具蛇が登場することによりもと《見蛇楽》と言われてきたが、10世紀ごろまでは確かに存在する演目であることが明らかとなった。さらに、中国の古文献より、《還城楽》それ自体の演目の存在が明らかとなり、つまり、現在の《還城楽》は2つの演目がその起源にあるということを明らかにできた。また、譜字分析による動作分析によって、舞楽《還城楽》の動作と構造は2つの場面で対照的な特徴を抽出することができ、複相的な関係を明らかにできた。
　したがって、舞楽《還城楽》は起源においても舞踊構造においても複相性を持つということができる。

　Genjo-raku is one of the existing Japanese court dances about whose origin there are some explanations. Moreover, it has a special structure in its dance performance when compared with other existing Japanese court dances. The purpose of this paper is to reveal duality in Genjo-raku, both in terms of its origin and dance structure.
　Research of the origin and dance structure was conducted in the following respective ways. Classic literature, both Japanese and Chinese, was scrutinized for the origin of Genjo-raku, while dance notation in Chinese characters and katakana that was recorded in the Meiji era(19th century) was analyzed for its dance structure and movement.

　　The results are as follows:
1. The origin of Genjo-raku has been often attributed to a dance called Kenja-raku due to the appearance of a wooden snake on the stage. Although at the present Kenja-raku does not exist, a Japanese literature-based investigation revealed that Kenja-raku had been an existent performance until around the first half of the 10th century in Japan. On the other hand, a Chinese literature-based investigation revealed that during Tang Dynasty in China a performance called (Dosho-)Genjo-raku was one of the official programs registered to the imperial court at the end of the 6th Emperor Xuan Zong's era in the 8th century. Considering the above-mentioned, it is presumed that Genjo-raku was a piece of (Dosho-)Genjo-raku, a grand performance. Therefore, the present Japanese Genjo-raku has two origins, Kenja-raku and (Dosho-)Genjo-raku.
2. Characteristics of the movements and of the structure in two main parts of Genjo-raku were examined by analyzing dance notations individually. It was proved by this analysis that there is a difference in the movements and structure of the two main parts.

　Thus, literature-based research, which places the origin of Genjo-raku in two kinds of dance, has revealed a duality in this court dance. Moreover, this duality has been confirmed in the contrasting relationship between the two main parts by the analysis of the dance notation. In this way, it may be concluded that the Japanese court dance Genjo-raku is a performance that is characterized by duality..