The Court』s main activities in Civil Procedure are to determine facts and to apply the laws, in which the former is prerequisite to the latter. Thus, there is no doubt about the importance of fact-determining in Civil Procedure. Although the Law of Civil Procedure has already provided some methods and procedure to determine facts, how exactly should the Court decide on the truthfulness of fact, i.e., what level of proof is required to reach a verdict, still remains in dispute. Theories such as 「almost confirmed truthfulness」, 「superior probability and 「high probability beyond common doubt」 are provided to solve this issue. But because these theories are still very abstract, the risk of judges』 arbitrariness still remain. The uncertainty and the difficulty to review any verdict even cause the distrust on the court among the public. To solve this problem, the theory of 「reliable level of proof」 has been brought up. This research project will review articles from Germany, Austria, and the Switzland. It will analyze the function, standard, and exceptions to the requirment of proof. By linking the jurisprudence practice of the Court, we hope to clarify this issue and build up a reasonable standard.