Background: Child Psychotherapy Facilities in Japan are child welfare facilities as defined by the Child Welfare Act. These facilities provide comprehensive treatment and support for children experiencing psychological difficulties that interfere with various aspects of daily life. They aim to improve children's situations through group living while providing psychological therapy, thereby assisting their growth, development, and independence. Given the nature of this facility, psychological care is positioned as extremely important. While there is prior research on music therapy practice by Osada et al. (2007), such studies are very limited.Purpose and Method: Ueno and Suga, together with Shimada, a psychologist at Child Psychotherapy Facility A, conducted group and individual music therapy sessions with Riko (pseudonym), a junior high school student, from September 2023 to February 2025. This study analyzes audio recordings, behavioral records (indexes) of Riko and the therapists, and conference notes. Based on this analysis, it examines the potential role music therapy can fulfill as a form of psychological care within Child Psychotherapy Facility.Results: The progression of music therapy and Riko's changes can be divided into the following four phases. Phase I: Resistance and opposition due to anxiety within group sessions, and adaptation to the music therapy setting. Phase II: Developing interest in improvisational expression. Phase III: Creating musical stories within individual sessions and singing expressions projecting herself. Phase IV: Improvising musical expressions of anxiety and underlying emotions. During Phase I, Riko showed resistance, such as deliberately playing loudly when the therapist asked her to play softly. However, after experiencing playing instruments improvisationally in Phase II without feeling tense, she began expressing her feelings through singing, playing instruments, and dancing in Phases III and IV.Conclusions: Music therapy as psychological care within the Child Psychotherapy Facility served as a space where Riko could express her complex emotions—difficult to verbalize—through music as a medium and build relationships with others through nonverbal communication. For Riko, music therapy was an extraordinary experience, and Shimada's presence was crucial in connecting it to her daily life. Shimada shared details about Riko's life within the facility and her school experiences. Her insights, offered from a psychologist's perspective on Riko's musical expressions, enabled a multifaceted analysis of Riko's musical expressions. Moving forward, we intend to implement music therapy in collaboration with facilities and schools, leveraging the unique characteristics of the Child Psychotherapy Facility as a comprehensive therapeutic environment.