This study applied a qualitative approach and investigated the processes of motivational change through goal setting in extensive reading (ER). The one-year ER program integrating goal setting was introduced in a Japanese university. Interviews were conducted with four selected participants from among 23 students. The results revealed different patterns in students' motivational change associated with goal setting. When students used goal setting effectively, they felt a sense of achievement, enhanced their intrinsic motivation and self-efficacy, and formed a virtuous cycle toward new goals. On the other hand, when students were unable to use goal setting effectively, they repeatedly failed to achieve goals and seemed less motivated to read. This paper discusses ways to set appropriate goals for increasing reading motivation.