本論文主要在於整理並分析我國行政程序法第一百三十五條以下有關行政契約之規定對於國內行政與司法實務的實際影響；而經過本文研究後，則發現：行政程序法迄今施行雖四年有餘，惟實務上對於相關問題之爭議，大抵仍集中在行政機關所締結之契約，究竟是為「公法」契約—亦即「行政契約」，抑或只是單純之「私法」契約的議題上。換言之，公、私法契約之判別，至今始終是我國行政與司法實務所遭遇到的最大困難。從而，面對實務的窘境，本文遂提出以契約主體為原則，契約標的為例外的「契約主體推定說」，來簡化公、私法契約區別的標準：凡行政機關所締結之契約，原則上推定為行政契約；只有契約所規範之法律關係全體均指向私法時，始例外地反證為私法契約。此說不但能有效地解決公、私法契約判別的困難，在實際操作下，或許更能符合公、私法契約區別的實益。

The main purpose of this paper is to see into the regulations of administrative contracts under the 135th to the 149th articles of our Administrative Procedure Law, in order to organize and analyze the factual influence of such regulations on domestic administrative and judicial practices. As this study goes, it reveals that while the Administrative Procedure Law has been put into practice for more than 4 years, the arguments over practical issues mostly center on whether contracts signed by administrative organizations are contracts in public law (namely “administrative contracts") or simply contracts in private law. In other words, to make a distinction between contracts in public law and contracts in private law has always been the greatest difficulty in our country's administrative and judicial practices, even up to the present time. Seeing such practical difficulties, this paper therefore proposes the theory of "inference from the subject in contract," which views the subject in a contract as the principal, and the object as the exceptional. Such inference will simplify the standard of making a distinction between contracts in public law and contracts in private law: whatever contracts signed by administrative organizations are inferred in principle to be administrative contracts; only when in a contract the judicially related whole — the part of rights and the other of duties as well — is leading to the private law, will the contract be exceptionally concluded to be a contract in the private law. This theory thus not only can solve the difficulty of making a distinction between contracts in public law and contracts in private law, but in practice also can bring about actual benefits resulting from such a distinction.