The purpose of this paper is to clarify the role of evidence in discussing social problems in the discipline of sociology. Social constructionism, which is the most influential perspective on the study of social problems, has kept some distance from the objective state. In this paper, on the other hand, we would like to focus on how the objective state is being useful by referring "judo death", a social problem which has arisen in the last few years. Since 1983, in Japan's schools more than 100 students has died of judo practice in afterschoolactivities. In 2011-2012, people paid much attention to "judo death", bringing the reform of both judo federation and school judo activities. The key of the reform was reducing head injury while doing judo. As a result there have been no death cases since 2012. By referring this judo death problem, we can pick up two roles of evidence on social problem. 1) Evidence is an important factor for the arising of social problem. It is also required for evaluating to what extent the problem is solved. 2) Evidence plays an essential role to bring t he expectation of solution.