The purpose of this study is to verify the mediated effect of a professional self-efficacy and an interpersonal relationship disposition in the effects of a family origin experience of a music therapist and a music therapy intern on the therapeutic alliance in the music therapy. The target of the study are music therapy interns and 121 licensed music therapists practicing all throughout the country, and this study statistically verified the survey data collected from the target using a structural equation. The results from this study is as follows. First, although the family origin experience of the music therapists and the music therapy interns do not have a meaningful effect on the therapeutic alliance in the music therapy directly, they do have a meaningful effect indirectly through the professional self-efficacy and the interpersonal relation disposition. Second, the professional self-efficacy completely mediates the effect of a family of origin experience on the therapeutic alliance in the music therapy. Third, the interpersonal relation disposition completely mediates the effects of a family of origin experience on the therapeutic alliance in the music therapy. The result of this study is meaningful in showing that even if a family of origin experience is negative, when a high professional self-efficacy and an interpersonal relationship are developed through proper therapist training and sufficient education, it could lead to a positive effect on the therapeutic alliance in the music therapy.