抵銷制度所具有之簡易清償機能與公平維持機能已廣受我國學說與實務承認，惟抵銷制度是否具有擔保機能一事，則尚未受到充分之關注與討論而仍存有疑義。 所謂抵銷之擔保機能者，係指在互有相對立債權債務的主被動債權人間，若被動債權人資力不足且同時對多數債權人負有債務時，身為多數債權人之一的主動債權人，可藉由抵銷權之行使，使其與被動債權人間相對立之債務立即消滅，產生主動債權人藉由抵銷權之行使，令自身債權獲得較其他債權人優先受償、主動債權如同受被動債權擔保般的效果。 此一抵銷權之擔保機能反映在法律規定上，與之關連最密切者，乃民法第340條。蓋民法第340條乃規範多數債權人（扣押債權人與主動債權人）於競爭何人得自被動債權人財產受償時，抵銷權行使應否受限制的問題。因此，若承認擔保機能為抵銷制度之本質機能，則在民法第340條之解釋適用上，即應擴大允許被動債權受扣押後抵銷權之行使範圍，使此一抵銷制度之本質機能得以充分發揮。 然觀察我國法將發現，目前我國學說對於抵銷制度本質上是否具有擔保機能，討論仍極為有限，此種討論不足的情況延伸至審判實務上，使各級法院在解釋適用民法第340條時，因欠缺理論基礎，導致對系爭條文之解釋適用存在有見解分歧、法律適用不安定的問題，凸顯了對於抵銷之擔保機能進行深入研究，並統一民法第340條解釋適用之必要性。 對上述問題，因日本民法第511條與我國民法第340條規範幾近相同，且該國判例學說長期以來已累積豐富之討論成果，可為我國法解釋適用之參考。在整理該國判例學說與修法動態後，可得出下列三點啟發：第一、「擔保機能」僅是多種「抵銷對第三人效力理論基礎」的可能選項之一，其存在對於抵銷制度並非絕對。第二、日本法上對於民法第511條之所以存在多種解釋方法，此亦係肇因於其背後對於「抵銷對第三人效力理論基礎」的選擇不同所致。第三、在決定是否以「抵銷制度本質具擔保機能」作為「抵銷對第三人效力理論基礎」後，尚須注意此一結論是否能與扣押命令效力範圍、民法第511條之體系定位、期限利益喪失約款之對第三人效力等周邊問題建立邏輯一貫而無矛盾的解釋。 將對日本法之研究成果運用在我國法的解釋適用上，可自民法第299條第2項之規範方式推知我國立法者有意採取「對抵銷期待利益之保護」作為「抵銷對第三人效力理論基礎」。考量民法第340條與民法第299條第2項同為抵銷制度下「抵銷對第三人效力」規範，故兩規範在解釋適用上應採取相同之理論基礎。換言之，民法第340條所規範的「抵銷與扣押」關係中，主動債權人之所以可藉由主張抵銷而獲得較扣押債權人優先受償的類似擔保效果，實為保障主動債權人對抵銷之期待利益所產生的事實上反射效果，並非抵銷制度本質上有何擔保機能存在。而在否定抵銷制度本質上具有擔保機能後，則可以此結論作為解決相關問題之起點，逐一推論出民法第340條應如何解釋適用，以及其他周邊問題的解答。 / Expediency in satisfying debts and keeping fair treatment among creditors are two major functions well acknowledged by academics and the judiciary in Taiwan. However, a possible third function - securing unpaid loans through claiming an offset (hereinafter referred to as securing function) - has not yet been fully discussed. The purpose of this thesis is to fill this gap in the understanding of the issue. Securing function of offset means that in the situation that two people are each others’ creditors and one of them is insolvent, the solvent creditor can assert their right of offset. To claim an offset allows a creditor/debtor to have his/her unpaid loans preferentially satisfied before other creditors’ claims. Allowing a creditor to claim offset results in the same effect as the creditors’ loan having been secured. In the civil code of the R.O.C, Article 340 is most relevant to the question of whether the right of offset includes the securing function. Article 340 stipulates that, “When an obligation has been attached by an order of the court, the third debtor of such obligation shall not take a claim which he has acquired from the creditor after the attachment to offset the obligation attached.” The question in point is: • whether the limitation on the garnishee’s right of offset is only limited to his counter claim against his creditor generated after the issuance of an attachment order, or • should it be expanded to all of his counter claims, including those generated before the issuance of an attachment order. The key to answer the abovementioned question lies in whether securing function is within the intention of the legislator in enacting Article 340 of the Civil Code of the R.O.C. After scrutinizing essays related to the right of offset in the Civil Code of the R.O.C., it is clear that scholars in Taiwan have not discussed the questions enough yet. The lack of academic research results in considerable confusion in judicial practices when applying Article 340 of the Civil Code of the R.O.C. Japanese scholars and legal precedents of the Japanese Supreme Court have been exploring the securing function issue of the right of offset for more than half a century. There is the same question regarding Article 511 of the Japanese Civil Code, and the article is almost identical to Article 340 of the R.O.C Civil Code. We consider it to be helpful to review their research and take it as our reference. The gist of Japanese academic research and legal precedents regarding the above-mentioned issue, can be summarized as follows. First, acknowledging securing function of the offset right is not necessary in constructing the theory of the right of offset; second, explanations for Article 511 of the Japanese Civil Code in Japan have not yet been unified. There are still controversies in Japanese scholars' research and legal precedents regarding the issue, as Japanese scholars and Japan's Supreme Court continue to offer various theories regarding the legislative intent of Article 511. Third, whether securing function can be considered as within the legislative intent of Article 511 further relates to the solutions to the following three questions: the scope of attachment orders, the role of the right of offset within the whole of the Japanese civil law system, and the influence of acceleration clauses. The above-mentioned research on Japanese law concludes that the legislative intent of the Japanese Civil Code is not to confer securing function to the right of offset, but to protect legitimate expectations of the debtors to have the chance of claiming offset. The same conclusion can be derived from observing the design of paragraph 2 of Article 299 of the Civil Code of the R.O.C., which regulates the influence of the right of offset on the third party creditors (hereinafter the “third party effect”). Paragraph 2 of Article 299 stipulates that, “At the time of the debtor being notified, if the debtor had the claim against the transferor [sic], and if such claim matures before or at the same time as the claim transferred does, he/she may claim for offset against the transferee.” To clarify, when a debt is transferred from the original creditor to a new creditor (hereinafter transferee), the debtor can only claim an offset against the transferee with a counter claim that matures before or at the same time as the transferred claim does. The same design in the Japanese law leads to the conclusion that the legislative intent in designing the third party effect of the right of offset is based on protecting the legitimate expectation of the debtor in having the chance to claim the right of offset. We propose that it is helpful to construe Taiwan’s system in the same way. To clarify the conclusion further, Paragraph 2 of Article 299 and Article 340 of the Civil Code of the R.O.C. both regulate the third party effect of the right of offset. The same theory of interpretation should be adopted in order to keep the Taiwanese civil law system coherent. Article 340 provides that a garnishee can only claim the right of offset when his/her counter claim against the creditors originated before the date of issuance of the attachment order. We should construe that the legislative intent is to protect debtors’ expectation of a chance to claim an offset identical to the construction of the paragraph 2 of Article 299. Although the operation of Article 340 allows the debtor/creditor to satisfy his/her claim preferentially before other creditors under some circumstances, the so-called “securing function” of right of offset can only be considered as a collateral effect and is not within the legislative intent of the regulation. After denying the legislative intent of securing function of the right of offset, the thesis further clarifies the answers to three questions relating to the third party effect of the right of offset: (1) the limitation on the right of offset stipulated in Article 340 shall be construed as an exception in the civil law system of Taiwan; (2) the scope of an attachment order shall not reach the right of offset of the third party (garnishee) in principle; and (3) the acceleration clause shall not influence the rights of third parties.