本文係將代理理論中主理人與代理人間的契約關係，用於銀行放款市場中銀行（主理人）與借款者（代理人）上。並探討在獨佔銀行的產業結構下，當借貸雙方存在「資訊不對稱」情況時，如何運用契約的「自我選擇」機能來防止逆選擇問題發生。本文分別探討了完全訊息與不完全訊息下，二種類型及無限多種類型借款者之情況，並推導出最佳契約及次佳契約的設計原則。

This paper attempts to apply the principal-agent model to banking firms and borrowers in loan market. It inspects when asymmetric information exists in monopoly banking industry, how to use self-selection mechanism to protect adverse selection happening. It developes two types and infinite types of borrowers in perfect information and imperfect information, and decides the designing rule of optimal contract and second-best contract.