Act Governing the Choice of Law in Civil Matters Involving Foreign Elements Article 18
Where an agent undertakes a juridical act in the name of the principal with a third person, as between the principal and the third person, the existence, extent, and effect of an exercise of the agent’s authority are governed by the law as expressly chosen by the principal and the third person; in the absence of an express choice, by the law of the place with which the act undertaken by the agent is most closely connected.
中文原文 涉外民事法律適用法第18條
代理人以本人之名義與相對人為法律行為時，在本人與相對人間，關於代理權之有無、限制及行使代理權所生之法律效果，依本人與相對人所明示合意應適用之法律；無明示之合意者，依與代理行為關係最切地之法律。