A criminal proceeding is a procedure by which the power of criminal punishment of the State may be enforced. However, what the object of such punishing power would be has long relied on the concept of the unit and identity of case. After reviewing the history of criminal procedure law compared to its counterpart in Japan, the related legal development has deeply been influenced by Japan since the era of late Ching dynasty. However, while the Japanese criminal justice system was drastically changed by the United States immediately after World War II, the ROC counterpart has remained its pre-war inquisitorial tradition mainly based on the old fashion concept of the unit and identity of case. This study claims, after identifying the inquisitorial element behind the pre-war justice system, that the scope of trial should be determined on the principle of Separation of Power, and should be subject to the principle of the Double Jeopardy. In addition, there will be no practical problem if res judicata could be conditioned on trying all facts in a single punishment case.