The purpose of this study was to identify the offering and operation of music elective courses in the inter-school joint curriculum according to the implementation of the high school credit system. In addition to the trend of opening music electives courses and the number of schools in the inter-school joint curriculum from 2020 to 2021, the operation status was analyzed by music electives courses, subject organization, city and province, school characteristics, and online and offline types. As a result, the number of music elective courses increased in 2021 compared to the previous year, and it was found that major practical skills, music theory, sight singing & ear training, performance practice, and music history classified as Specialized subjects I were established. The average number of courses opened by city and province was about 3 with a wide variation. Most of them were large-scale schools located in large cities, or designated as leading schools in an offline system.