In Japanese judicial reform, the Diet approved bills concerning the new mixed jury system, "Saiban'in-seido," in May 2004. In this system, citizens will be selected from voter's lists for participating in judicial panels. And those lay persons and professional judges will deliberate serious criminal cases. They are to deliberate, together with professional judges, to make decisions on a serious criminal case. In running this system, lay persons and professional judges are expected to cooperate effectively in their deliberations. To achieve effective cooperation, judges' perceptions of citizens will be important because their perception is anticipated to affect judges' behavior.