Active learning classes, which aim at increasing student participation in class, demand more management skills from the instructor than a conventional lecture class does. However, the instructor rarely recognizes how his/her lessons are different from those of others. The instructor cannot know exactly how one of his/her lessons is different from his/her previous week's lesson. This class-to-class comparison is effective in improving classes. This paper proposes a method for automatically visualizing the process and content of classes. Although there are ways to visualize the contents of classes manually, these approaches involve considerable investments of time and money. Machine learning techniques can automate the visualization. Our method estimated content with an average accuracy of 72.4%. Through our visualization, we confirmed that individual instructors use time differently from others and use their own time differently from lesson to lesson.