This study seeks to understand what life a secondary school teacher experiences as a teacher in an IB school introduced to public education. Since Daegu City and Jeju Island introduced IB education into public education in 2019, IB education has been spreading nationwide. In this situation, it is of great significance to understand what experiences general public education teachers who teach based on the national curriculum have while operating the IB MYP curriculum and what kind of life they create as teachers. To achieve this research objective, a middle school teacher who had worked at an IB school in Daegu City for 5 years was selected as a research participant and an in-depth interview method was used. As a result of the study, first, the research participants experienced conflict between grade-based education and inquiry-based education at IB schools. Second, research participants experienced that the IB unitplan was a powerful tool that improved teacher expertise and led to inquiry-oriented classes. Third, the research participant came to recognize the possibility that she could maintain her life as a subject expert even as she grew older. Based on the above, it was discussed that a unitplan that supports the application of the national curriculum to school sites must be developed, that support for IB unit design for teachers is necessary, and that an appropriate response to the entrance exam culture is necessary to enhance IB education.