This study empirically analyzes the impact of coaching service quality on adult learners’ job preparation behavior and examines the mediating effect of learning immersion and the moderating effect of social support to derive implications that can provide more practical help in improving the coaching service quality of lifelong education institutions. At a time when the importance of coaching and career counseling for adult learners’ job preparation in lifelong education institutions is emerging, there is a lack of research on the structure of coaching service quality. On the other hand, although social support is an important variable as a social and environmental factor as well as an individual characteristic factor, there is a lack of research on it as a moderating variable. Accordingly, this study presents the dimensions of coaching service quality of lifelong education institutions based on previous research on coaching service quality that emphasizes traditional service quality and the concept of coaching, and analyzes the relationship with adult learners’ job preparation behavior to clarify not only the service quality provided through the system but also the mediating effect of adult learners’ learning immersion, while simultaneously analyzing the moderating effect of social support. The data for this study is selected as research subjects from adult learners who use lifelong education institutions located in Seoul, Gyeonggi, and the metropolitan area in Korea. The research model was analyzed using the IBM SPSS Ver. 23.0 program and the PROCESS Macro Ver. 4.3. Specific statistical techniques include frequency analysis and correlation analysis of the research variables of coaching service quality, learning immersion, job preparation behavior, and social support, hierarchical regression analysis to confirm the mediating effect of learning immersion, and model verification of the PROCESS macro to confirm the moderated mediating effect of the research model.