In this study, we propose an interactive dance training support system to promote an individual's motivation for practicing dance. In order to motivate the user, we designe a scenario of dancing with friends (virtual characters) by adopting a projection-mapping technique to create a large-scale augmented reality space. We project the dancing scene on a three-sided wall-type transparent screen to improve the sense of immersion. The proposed system assigns scores by comparison of the user's movement to a target dance movement in real-time. The reactions of the projected characters provide feedback to the user interactively according to the calculated score. The advisor character can verbally encourage the user when the scores are low. Finally, we conduct a user study to verify the usefulness of the proposed system.