This study aims to explore the difficulties faced by music teachers with a background in Western music when teaching traditional Korean music (gugak) in schools and to draw educational implications from these findings. The study involved six middle school music teachers who majored in Western music, and data were collected through in-depth interviews and teaching materials provided by the teachers. The research participants' experiences related to Korean traditional music classes were explored by asking open-ended questions about what Korean traditional music classes were and what kind of teachers they wanted to become, and as a result, the experiences and perceptions related to teachers' professional formation were analyzed into five categories, 11 thematic groups, and 55 topics. In order to understand the nature of the difficulties in teaching Korean music, a music teacher who majored in Western music was selected as a case study and analyzed using a qualitative research method, and the results are as follows. First, during their university years before becoming teachers, the study participants who majored in Western music felt a sense of unfamiliarity when they first took a traditional Korean music (gugak) class. Second, the nature of the difficulties in teaching Korean music experienced by the participants in the study was not about knowledge, but about what to teach. Third, the study participants became teachers and worked tirelessly to overcome difficulties and implement good Korean music lessons. Fourth, the study participants' identity as music teachers who teach national music was naturally formed through their Korean music lessons.