行政機關作成決定時，必須依據正確之事實。因此，行政機關本於其職權，須運用各種證據方法，以釐清事實，進行評價，並形成心證，最終作成預期之決定。有關行政機關調查之事項，一般歸諸行政調查之領域。我國有關行政調查之規範，目前尚乏統一之法典，係散見於不同之專業法規中。行政程序法自第36條至第43條，即係有關事實及證據調查之一般性規定。 行政機關從事調查時，行政程序法第36條係採行職權調查主義。由於在行政程序中之職權調查，涉及各種調查手段之使用，以及調查事實之責任，對事實之釐清及最終之決定有重大影響，自有必要對其內涵有深入之了解。其次，行政機關本於職權，固然有義務調查證據以釐清事實。惟此種調查義務之履行，應非毫無止境。 為了解職權調查之概念及範圍，本文乃分成下列數點：首先界定行政調查之概念，確立行政調查之意義，並就與職權調查相關之重要事項，如職權調查主義、自由心證原則及事實調查之瑕疵等，從事必要之探究。其次，會涉及到舉證責任的問題，亦有探討之必要。再者，將就確定行政調查範圍之重要標準，即決定重要性、證據必要性、比例原則及當事人之協力義務等，依序分別析論之。並將以最高行政法院近幾年來相關之裁判為評析之對象，期能了解司法實務之見解。最終將提出檢討及建議，以有助於我國此領域法制之進展。

It depends on the correct facts to make correct decisions for administrative agency. So it is necessary for administrative agency to clean facts, and administrative agency will valuate to form the opinions to make decisions. In Taiwan, the codes of administrative investigation is not available until now, but spreads on different areas of laws and regulations. The articls36-43 of the administrative process law are the general regulations of administrative investigation of the facts and evidence. The articles 36 of the administrative process law is the ”administrative authority investigation”. While administrative authority investigation concerns about different means and responsibilities of investigations, it is necessary to understand the connotations of it. Secondly, it is the duty of administrative agency to invest the different kinds of evidence, but it still has the limitation. To clarify the concept and the range of the administrative authority investigation, this thesis consists of several points below: first of all, this thesis would like to establish the concept of administrative authority investigation, and doing necessary researches of administrative authority investigation. Secondly, this thesis would analyze the indispensable standards as ”evidence necessary” ”principle of proportionality” Duty of cooperation” etc. This thesis would also analyze the recent judgments of the Supreme Administrative Court. We hope we could offer some advises to advance the fragments of laws in our country.