「車牌辨識系統」簡稱為「N系統」，將之運用於偵查者，即所謂「N系統偵查」。我國警方雖早有運用N系統偵查，惟就其適法性問題，卻鮮有討論者，本文之目的即在深入討論此一問題，具體上，提出三項設問:第一，N系統偵查侵害何種權利；第二，在N系統偵查之情形，應如何劃定公共場域中的權利保障範圍；第三，N系統偵查是否該當於個人資料保護法第16條第2款所定之情形。前兩項係屬於N系統偵查之侵害性問題，第三項則係有關N系統偵查的授權依據（法規範）問題。於此前提下，本文借鏡日本與德國之相關議論，從比較法的觀點進行分析與檢討，再以之為基礎，提出適法性判斷之兩階段構造並具體化其內涵。作者主張，N系統偵查之侵害性應區分四個階段（即「設備裝置」、「取得資訊」、「儲存累積」及「照合分析」四階段）來判斷，而其實施的授權依據之規範要求則會因N系統偵查之法定性（強制處分或任意處分）不同而有異，並由此導出前揭三項設問之解答作結。

The “license plate recognition system” is referred to as the “N-system” for short. Those implemented for the purpose of investigation are the so-called “N-system investigations”. Although the police in our country have used the N-system for investigations, there has been little discussion about its legality. The purpose of this paper is to discuss this issue in depth. The author raises three questions. The first, what rights are violated by the N-system investigations. The second, in the case of N-system investigations, how to define the scope of rights protection in the public domain. Finally, whether the N-system investigations could be under the circumstances set out in Art. 16(2) PDPA (Personal Data Protection Act). The first two questions are about the assessment of the quality and quantity of rights violations caused by the N-system investigations. The last question is about the review of the authorization basis (legal norms) required for the implementation of the N-system investigations. On this premise, this article conducts an analysis and review of comparative law. Specifically, first discuss the relevant arguments of Japanese law, then discuss the related viewpoints of German law, and finally put forward the insights of this article. Namely, the author advocates that the Legitimacy Judgment Process of the N-system investigations should adopt a two-stage structure. And then further concretize the connotation of the judgment elements at each stage. The author concludes that the invasiveness of the N-system investigations should be judged in four stages: installation stage, acquisition stage, storage phase, database comparative analysis stage, and also pointed out that the implementation of the N-system investigations will be different in terms of the legal requirements on the basis of authorization due to its legal nature (prosecutors' order or non-prosecutors' order). In the end, the author derives the answers to the three previous questions from this proposition.