Since 1350(庚寅年), the invasion of Waegu on the Korean Peninsula has skyrocketed. In Goryeo Government, when the damage became large, information was collected through the captured Waegu and the prisoners, and negotiations with Japan began in earnest from 1366. Initially, the Joseon side was negotiating with the Muromachi Shogunate to crack down on Waegu and repatriate Waegu prisoners. However, around 1377, the amount of diplomatic power was concentrated on the influential people in Cyuugoku and Kyushu, where there are many bases of Waegu. Regarding negotiations with Japan since the 14th century, the “Tonshinsa”(通信使) dispatched by the King of Goryeo and Joseon to the ‘King of Japan'(幕府將軍)has been attracting attention. As a premise, cases of dispatching diplomatic missions in the latter half of the 14th century have been considered. This study focuses on diplomatic negotiations and envoys to Japan in the late Goryeo and early days of Joseon. Along with the name of the envoy, we specifically examined the recognition of Waegu in Japan and Joseon, the negotiations with Japan on the Joseon side, and the response on the Japanese side.