This study delves into what should comprise the Specialized Contents Related to the Subject (Music) in elementary school teacher training. The Central Council for Education’s 2015 report, “Improvement in competency of teachers who will carry forward future education in schools,” suggested the following new directions for changes in teacher training: i.e., (1) to enlarge the categories for specialties or to integrate subjects within teacher training courses and (2) to prepare policies to organize the core curricula for teacher training courses. In 2017, Hiroshima University was assigned a project for integral reform of the promotion of teacher development, employment, and training for career advancement. Our team drew up a plan for the core curriculum for the Specialized Contents Related to the Subject (Music) in elementary school teacher training. This study compares this new curriculum with two other plans and examines all curricula from several perspectives. The results show that the standard for the core curriculum subjects has become a double-edged sword. Teacher trainers should refer to this standard in developing their own contents and teaching methods for student teachers.