The Tokugawa Art Museum possesses many instruments used in gagaku and nohgaku. We investigated nohkan, ryuteki and hitoyogiri flutes in the Museum’s collection. Of the two nohkan in the collection, one named “Semiore” with a certificate of authenticity by the master Seibei VII of Fujita School of Noh is said to have been made by Shishida. Radiographs of this nohkan taken with the cooperation of researchers Otsuka and Matsushima at the Center for Conservation Science and Restoration Techniques revealed that it was made not by using the conventional method but by using a single thick bamboo material. The small inner diameter of the nohkan between the hole for the mouth and first finger hole contributes to unique, sharp sound of the nohkan. While the conventional method involves inserting a separate piece called nodo (throat) into this portion, no sign of such a piece having been fitted was discovered. This points to the existence of a different method for making nohkan. According to some researchers, nohkan with a small inner diameter is a result of some incident in repairing a broken ryuteki. Our finding suggests that this theory needs to be corrected.