所謂無權代理人之法定擔保責任，係指法律規定代理人應擔保代理權限存在；否則，無權代理人應使善意相對人所處之法律上地位，如同無權代理人具有代理權一樣。換言之，善意相對人對無權代理人之請求，係以代理人具有代理權或本人承認無權代理行為時，善意相對人得請求本人給付之範圍為限。本人如果契約不履行，原則上僅負過失之損害賠償責任。然而，最高法院五十六年臺上字第三○五號判例，卻使無權代理人負無過失之損害賠償責任，因此值得進一步研究。債務人賠償債權人履行利益，前提要件是，契約有效成立。然而，無權代理人所訂立之契約，本人拒絕承認時，效力不及於本人，亦不及於代理人。最高法院九○年度臺上字第一九二三號判決使無權代理人負履行利益之損害賠償責任，亦有研究之空間。 An agent's warranty of authority refers to the situation in which an agent warrants-to all who deal with him in that capacity-that he has the authority which he assumes; otherwise, the unauthorized agent is responsible for his acts in the course of his agency, leaving the legal status of his contracting party unchanged. The bona fide contracting party's claim to the unauthorized agent is limited to the performance of the principal under the circumstances that the agent is authorized or that unauthorized acts of agents are ratified by the principal. When the principal breaches the contract, in principle, only negligence would be pursued. Why, then, does a precedent laid down by the Supreme Court in 1967 found that strict liability should be imposed upon the unauthorized agent for damages? Article 110 of the Civil Code does not expressly provide the imposition of strict liability on an unauthorized agent for damages. Why does the said Supreme Court precedent ruled that the liability of the unauthorized agent is a special liability based on the provisions of the Civil Code and is categorized as strict liability? Expectation damages refer to the value that the creditor would have realized had the contract, after its conclusion, been fulfilled by the debtor. In other words, the prerequisite for a debtor to pay a creditor expectation damages is that a contract must be effective. Without the principal's ratification, the contract signed by the unauthorized agent binds neither the principal nor the agent. Why does a decision given by the Supreme Court in 2001 make the unauthorized agent liable for expectation damages? Because provisions of the Civil Code and theories in Taiwan are mostly rooted in those of European countries, to resolve the aforementioned questions, this study analyzes and reviews the laws in Taiwan by means of legal history and comparative legal studies of European countries.