Policy legitimation, a special policy is adopted by the government, is very important in the policy process. Without it, public acceptance of a policy is easily undermined. In Japan, a common method of policy legitimation is passage of a law by the Diet, but courts decisions also give legitimacy to public policy. Particularly in exercising the power of judicial review, courts can correct or void a public policy through interpreting the Constitution or laws. The judiciary, thus, has become an important policy-making forum. This paper focuses on the constitutional cases and studies judicial influence on public policy in Japan.