On May 2009, laws came into force in Japan to enable citizen participation by introducing lay judges in criminal courts. Lay judges, who are randomly selected out of the electoral register, comprise the majority of the judicial panel to help decide the outcome in trials for certain severe crimes. To make their own judicial decisions, lay judges must rely heavily on moral intuitions that are often driven by emotions, due to the lack of judicial expertise. Under what conditions can lay judges, guided by their emotions, come to reasonable decisions? What is the definition of rational emotions capable of guiding reasonable judicial decisions? These questions must be answered to make the lay judge system feasible. Recently, Martha C. Nussbaum, together with Dan M. Kahan, has developed a theory of emotion-based criminal judgment. In this paper I am going to answer above questions relying on Nussbaum’s theory of emotional judgments.