The well-established socio-educational model of second language learning motivation developed by R. C. Gardner was adapted and applied to study instrumental music learning motivation. The similarities between music and language suggested that the adaptation might lead to new insights in the study of music motivation. At the heart of the proposed model is a multifaceted description of the relationships among motivation, attitudes, anxiety, support from others, perceived competence, and achievement. A sample of 107 high school band students was selected to participate in this study. Results of a path analysis of questionnaire responses indicate that the adapted and expanded socio-educational model fit very well with the present data and described key motivational structures. The key support for motivation to learn was supplied by integrativeness (an interest in taking on the characteristics of musicians, positive attitudes toward learning instruments, and an interest in music learning), plus attitudes toward the learning situation (music teacher and course).