The adversary system is one of the major basic principles of the current criminal procedure law in Japan. However, our adversary system differs slightly from that originating in Anglo-American Law. In our system the adversary system tends to be identified limitedly as a mere skill or technique for proceeding a trial. We see there the lack of true understanding of the adversary system which originally brings core values such as fairness or impartiality to criminal procedure. Now, as Saibanin Saiban, our new lay judge system is becomes established, a new perspective for the adversary system is required. We have to look back upon the traditional arguments about the adversary system and determine its true meaning and function in order to revive not only our trial proceedings, but also the criminal justice system.