行政機關於從事行政調查時，經常會發現有涉及犯罪嫌疑之事實，此時即與刑事偵查有關。由於刑事偵查之目的、主體、方法及基本原則等，皆與行政調查不同，因此有必要劃出其與行政調查間之界限，以明確各該適用之範圍。此外，行政調查亦有可能同時兼具刑事偵查之性質。對於此種模糊地帶，亦有需要予以釐清，以避免行政機關假借較為寬鬆之行政調查程序，規避嚴格之刑事偵查限制，以遂行其刑事偵查目的，致侵害人民之權益。本文先說明行政調查與刑事偵查之基本概念，其次比較兩者間之重要差異，並針對何謂刑事訴訟法第228條第1項之「知有犯罪嫌疑」？前偵查程序與行政調查之關係，以及行政調查與刑事偵查之主體等，分別討論之。再就重要之刑事偵查程序之原則，如令狀原則及緘默權兩者，如何適用於行政調查析論之。期能藉此探討，有助於釐清行政調查與刑事偵查之界限。

The administrative authority may find facts involved with criminal suspects on administrative inquisition procedure. It is related to criminal investigation. Since the purpose, subject, measures and principles are different, it is necessary to make the limits clear to clarify the connotation.Moreover, it is possible to exist in both administrative inquisition and criminal investigation. To clear up the illegibility is also meaningful, which could prevent the administrative authority to evade the more rigorous limits of criminal investigation by means of loose administrative inquisition procedures, to infringe on the rights of citizens.This thesis explains the concepts of administrative inquisition and criminal investigation firstly. After that, we try to compare the important difference between both, and explain the concept of ”knows there is a suspicion of an offense having been committed” of Article 228 of The Code of Criminal Procedure. Then we discuss the relations and subjects of administrative inquisition and criminal investigation. Finally, this thesis conclud with how the basic principles as warrant requirement and the right of silence apply for the administrative inquisition procedure. We hope the points of view above could clarify the limits of administrative inquisition and criminal investigation.