刑事被告質問不利證人的權利，乃其訴訟上重要的防禦權，但為了秘密或被害證人之保護目的，或證人已不可及的現實理由，質問權利或其行使方式的限制，在所難免。如何以最小侵害手段，尋求個案的兩全之道，既是各內國法、也是國際人權法的重要議題。本文首先分析歐洲人權法院的案例法，指出限制的事由不但必須與質問保障具有等價關係，並且，必須針對具體個案指出充分、具體的限制理由。此外，無論偽裝措施或視訊傳輸，皆屬限制，法院必須依照個案情形，優先選擇較佳的防禦手段。就我國立法規定、司法解釋與實務裁判，整體而言，也遵循並確立了較佳防禦手段的優先性原則。藉由證人偽裝措施及視訊訊問等隔離措施的立法選項之創設，司法實務再三宣示，法院不應貿然選擇保障最差的剝奪質問選項。但是，實踐仍有美中不足之處，其中尤以次佳防禦手段的濫用危機，最為嚴重。例如，視訊訊問在欠缺等價事由的情況下，被濫用以取代當庭質問的最佳防禦手段。此外，秘密或被害證人的保護目的，抽象而言，固然可能作為限制質問的正當事由，但這無法免除針對系爭個案而具體、充分說明限制理由的必要性，這是審查密度問題，例如，以性侵被害人因身心創傷而無法出庭受質問為由，個案中至少應有專家的鑑定意見以資佐證，秘密證人匿名性的保護亦同。最後，由於我國立法多將蒙面、變聲、變像、視訊傳送等各種隔離措施併列規定，稍嫌籠統，因此法院同樣應該針對具體個案而個別審查的是，各種隔離措施的限制高低程度及其與限制目的的比例關係，如此才能於個案中找出最小侵害手段，真正實踐較佳防禦手段優先性原則。

In a criminal procedure, the right to confront a hostile witness is essential to a defendant. However, it is sometimes inevitable to restrict this right or the way to exercise it when a witness or victim should be kept anonymous or when a witness is in fact unavailable. Therefore, how to find a balance between the means and the end is a cardinal issue of domestic and international human rights law. This article firstly analyzes the case law of the ECHR and points out that the restriction and the protection of right to confront should be proportional. In addition, the author would like to suggest that there should be sufficient and substantial reasons in specific cases to justify the restriction. Furthermore, a court should choose a better defense method in each case. Generally speaking, as far as our statutes, judicial interpretations, and precedents are concerned, they entrench and conform to the principle of priority of taking the better defense for the accused. By disguise, video-conferencing, and other statutory options, the precedents repeatedly declare that a court should not rashly deprive a defendant of the right to confront a witness. Nevertheless, there is much room to improve, especially the overuse of the second best defense method. To name a few, face-to-face confrontation, the best defense method for a defendant, is often replaced by video-conferencing without sufficient reason. In addition, given that the protection of witnesses or victims may serve as justifiable reasons to restrict the right to confront, it is required to thoroughly and clearly articulate these reasons in concrete cases. Last but not the least, the related statute which lists various quarantine measures in the same provision is not clear enough. A court should review in each case the proportionality between the means and the end to find out the least restrictive measure. Only by doing so can we implement the priority of taking the better defense for the accused