To train as lifelong music learners, learners need to clarify the relationship between learning motivation and behavior. This study clarifies the relationship between learning motivation, enjoyment of learning, and active involvement/volition (effortful study and willpower to continue studying) in lifelong music learning by taking the Hiroshima University extension course “Let’s enjoy chorus.” Then we show the significance and problems with lifelong music learning in university extension courses. The targeted extension course is held for the public, even as a formal chorus class for music students and non-music students. Most of the learners in the extension course were in their 50s to 80s, and many of them had participated every year for more than three years. A questionnaire survey for 39 learners in the extension course was conducted. The questionnaires were constructed using three measures of “motivation” with five subscales, “enjoyment” with three subscales, and “active involvement/volition” with two subscales. Because of the examination, the motivation of “self-improvement orientation” had an impact on the enjoyment of “diverse thinking,” and the enjoyment of “knowing” had an impact on “volition.” Conversely, the motivation of “friendship orientation” did not affect any of the enjoyment factors. The findings suggest some significance and problems with music learning in a university extension course. The significance: lifelong learners can possess and develop the wisdom to respond to every situation in/out of music and have expertise in life when they participate in musical activities, acquiring new knowledge and experience they have never had before. The problem: coordinated efforts that encourage learners’ friendship orientation, for instance, by setting up an environment that encourages them to be active with others, are needed to make co-learning between lifelong learners and university students possible in a university extension course.