The pieces of daeyeop, considered as the original form of the classical vocal genre gagok, are very important sources that show the process through which Mandaeyeop in Geumhapjabo (the scores of plucked zither geomungo) was derived from “Jinjak” compiled in Daeakhubo (the scores of court music). This study aims to reveal the relationship of the melodies of Jinjak 3, Daeyeop, and Mandaeyeop, distinguishing daeyeop's melodic phrases and analyzing their melody structures. It focuses on four daeyeop pieces for analysis--Pyeongjodaeyeop from Siyonghyangakbo (lit. the Joseon-style scores used at the time), Daeyeop, Pyeongjodaeyeop aka Naksujo, and Daeyeop Kim Jong-son from Hyeongeumdongmunyugi (a collection of records and scores related to geomungo). The melody analysis in this study was conducted by distinguishing the structural notes from the melodic notes in the melody for each phrase and extracting the skeletal melody of the phrase unit connecting structural notes. As a result of extracting and comparing the skeletal melodies of Jinjak 3 and Mandaeyeop, it was found that the skeletal melodies of the second half of daeyeop and buyeop of Jinjak 3 were similar to chapters 3 to 5 of Mandaeyeop. As a result of classifying the phrases of the four daeyeop pieces and extracting and analyzing the skeletal melody for each phrase, the melodies of the four daeyeop pieces shows differences for each piece. Chapters 1 and 2 of the daeyeop pieces were not directly influenced by the melody of Jinjak 3, but similar skeletal melodies are used among the daeyeop pieces. Chapter 2 of the daeyeop pieces generally uses a changed one from the melody of Chapter 1, but the melodies of Chapters 1 and 2 of the daeyeop pieces in Hyeongeumdongmunyugi appear more similar than those in Pyeongjodaeyeop. The melodies of the daeyeop pieces show the greatest difference in chapter 3. In other words, while Chapter 3 of Pyeongjodaeyeop uses a melody similar to Jinjak 3, Chapter 3 of the three daeyeop pieces in Hyeongeumdongmunyugi uses similar melody to Chapter 5 of the same piece. The melody of Chapter 4 of the daeyeop pieces in Hyeongeumdongmunyugi uses higher notes than that of Chapter 4 of Pyeongjodaeyeop and has a complex form, so it is clearly distinguished from the melody of Chapter 5. In addition, the form of daeyeop pieces in Hyeongeumdongmunyugi continues to that of Mandaeyeop in Geumhapjabo. Therefore, it can be said that daeyeop pieces show a transitional period in which the form of Jinjak 3 was changed into that of Mandaeyeop. This study reveals that Pyeongjodaeyeop, which has a melody similar to that of Jinjak 3, was transformed into the daeyeop pieces of Hyeongeumdongmunyugi, which have a melody and form distinct from Jinjak 3, and then was established as Mandaeyeop in Geumhapjabo. In addition, it confirms that the daeyeop pieces in Hyeongeumdongmunyugi had a direct influence on the formation of Mandaeyeop.