按聯合行為之執法實務，因面臨直接證據取得不易之現實，各國執法機關與法院莫不仰賴間接證據以證明事業間存乎於心的「合意」，從而「合意」要件的認定，成為在認定聯合行為時，最艱困的挑戰。鑑於我國學說與實務，尚未就如何運用間接證據證明合意之存在，形成一套可資依循之操作法則，從而本文乃一秉經濟理論、法律理論並重，而兼採法律經濟分析之方法，參諸反托拉斯法施行歷史最久、執法經驗最為豐富之美國，分析觀察其理論與實務之發展，加之以大量案例之研析，歸納出其長期踐行所形成之操作原則，並於檢視我國聯合行為之實務運作情形後，在我國實定法律與執法實務之架構下，提出本文所建議之間接證據操作原則，期能供作我國行政院公平交易會與行政法院，於認定聯合行為案件「合意」要件時，可資依循之操作準則，相關操作準則之具體內容，則包括間接證據之類型化、不同類型間接證據之論究先後順序、經濟分析方法與經濟性證據之運用方式、評價經濟性證據時應採取之合理心證運作模式、為控制經濟性證據之無規則性本質而導致的法律不確定性風險，而就證據價值所為之必要限制、以及本於公平正義與效率之理念，而設定出之聯合行為行政訴訟之據證明度標準，及於該證明度標準下所形成之具體操作內涵。 關鍵字： 卡特爾、合意、間接證據、證明度標準、有意識平行行為、促進行為、附加因素 / The competition authorities and courts nowadays have difficulty to obtain direct evidence to prove a cartel’s agreement for horizontal conspiracies seldom entailing refined articulation of mutual understanding—often the understanding is no more than a wink or a nod, in this situation, inferring the conspiracy based on circumstantial evidence is the normality rather than the exception and has bedeviled the enforcer and courts when distinguishing between innocent interdependence and illegal conspiracy. In view of deficient in a systematic way for Taiwan Fair Trade Commission and the Administrative Courts in manipulating circumstantial evidence when proving the existence of an agreement, this thesis proposes a systematic mode and criteria of manipulating through surveying numerous horizontal restraint cases covering U.S. and Taiwan by means of equally emphasizing law theory and economic theory as well as the approach of economic analysis of law. And the contents includes classifying the types of circumstantial evidence, the proper and reasonable way of economic evidence evaluation, the essential conditions in the probative value of economic evidence in order to control the pitfalls of uncertainty in the law resulting from increased reliance on such evidence as well as the standard of proof which conforms to justice and efficiency imposing on a cartel administrative litigation, with regard to the main issues of the suggestion framework. Key words: cartel, agreement, circumstantial evidence, the standard of proof, conscious parallelism, facilitating practice, plus factor