信用限額(credit rationing)在訊息不對稱的借貸市場中為常見的現象。為改善此一現象，大部分的國家常會以貸款保證政策(loan guarantee program)干預市場，以期提昇生產效率或社會福利。然而現有文獻都著重於探討政府貸款保證政策對減緩信用限額的有效性，卻忽略貸款保證資金來源的可能影響。本文延續Bencivenga and Smith (1993)的架構將貸款保證資金以課工資所得稅的方式內生化。此一設定顯示貸款保證政策對經濟成長存有兩股相反的力量。一是在不扭曲誘因機制( incentive compatibility)下，貸款保證政策可以降低信用限額並促進經濟成長。另一方面，政府同時吸取體系內資源作為貸款保證資金的來源，使體系內可用資金減少，不利經濟成長。這兩股力量隱含著經濟體系可能存在一最適貸款保證比率。本文除得到政府最適貸款保證比率存在的條件外，也探討金融發展對最適貸款保證比率的影響。
This paper evaluates the effects of the government loan guarantee program, which is financed from income taxation. In contrast to recent literature whereby this program is financed using resources outside the economy. this paper finds that the loan guarantee program creates two opposite effects to the economy. An increase in the ratio that the government promises to guarantee loans, on the one hand, will reduce the amount of credit rationing, which is shown to facilitate capital accumulation and hence promote economic growth; on the other hand, such an increase induces the government to raise the income tax rate, leading to a distortion of the economy's capital accumulation. We find the conditions for the existence of the optimal loan guarantee ratio. In particular, this optimal ratio is found to inversely correlate with the indicator of financial development, implying that the government should reduce any intervention when its financial sectors are more developed. This observation is consistent with recent literature.