This report is to found "comparative study of theatrical arts", an entirely new field, and to develop its methodology. To my understanding, this field is essentially important not only to clarify each characteristics of various theatre forms, in the east and the west, but also to approach the fundamental conception of theatre art in general. There are at least three available methods : -(1) specific research of the influence between plays of two or more different countries, (2) to compare plays of different countries, independent to each other but having common dramatic moment or analogous style, (3) to find out the difference in terms of aesthetic sense from the reaction data of certain plays watched by foreign audience. Concrete subjects I have worked out with each method are as follows : -(1) baroque nature of the Japanese traditional theatres, Joruri (Bunraku) and Kabuki, induced from the study of "Hamlet" in Japan. (2) Essential character of tragedy in Joruri and Kabuki as "family tragedy of implicit understanding and acquiescence" in the case of "Imoseyama" compared with "Romeo and Juliet". (3) Universality and speciality of Kabuki induced from the reaction data of Kabuki abroad, in USA, USSR and west Europe, each of which I attended as a literary adviser. [Specific research published as "Hikaku Engeki-Gaku" (Grundlegung der vergleichenden Theaterwissenschaft). written by Kawatake, published by Nansosha, Tokyo.]