The most important element in the Cheoyongmu is the mask of Cheoyong. Even if all of the costumes are present, the performance is not considered Cheoyongmu without the mask. In the ninth volume of ancient record Akhak gwebeom, in the section titled “CheoyongGwanbokDoSeol,” the making of the mask is recorded in detail., as well as the costumes and accessories used in the Cheoyongmu. From 1394 to 1442 (Sejong ’24), Cheoyongmu actors were women; however, men performed the Cheoyongmu for 61 years, from 1443 (Sejong ’25) to 1504 (Yeonsan ’10). After that time, the Cheyongmu was performed by women again. As of 1504, the Cheoyong mask underwent a drastic development. The time-frame of this change was 11 years after the Akhakgwebeom was written. Under the Yeonsan kingdom, Cheoyongmu was recorded in greater detail, mainly because of the king’s great interest in the performance. The significant changes made to the Cheoyong mask also occurred because the performance attracted the king’s attention. One example of the change of the design can be found in the mask’s beard; in the description in “Pubyok pavilion banquet,” the Cheoyong mask has no beard, which is extraordinary because this became one of its most distinctive features. Another example is the protruding jaw of the mask. In the books of “Dobyoeng” and “Gyecheop,” the jaw part of the mask was significantly emphasized. All of these features contradict those mentioned in the Akhakgwebeom. The design of the Cheoyong mask was not concluded in the time of writing the Akhakgwebeom; instead, it underwent significant and constant change over time. During the Japanese occupationera, the mask design deviated from the original design used in the Chosun dynasty. The office of the “Aakubu” is known to have performed the Cheoyongmu; however, the mask and costumes were not consistent with the original version of the performance. This is considered to be a separate artwork rather than the Cheoyongmu. There is also a record showing that some Japanese people made Cheoyong masks in that era. Throughout the late Chosun dynasty, the design of the Cheoyong mask was distinct to what is believed to be the original. However, the exceptionally long jaw of the mask, as described in “Heon-jong-dae mu-sin-jin-chan-do-byung,” is no longer reproduced. Regarding the changes of the mask in this era, it the true original design of the Cheoyong mask remains controversial. This represents another cultural disturbance stemming from the enforced occupancy by Japan. In this regard, the study of the Cheoyong mask represents the recovery of the distorted tradition of our country. From studying the Akhakgwebeom, as well as other historical records, we are finding out about a variety of original designs of the Cheoyong mask, including a humorous version from the Chosun dynasty era.