政府透過各類租稅優惠以促進投資的作法，在世界各國均甚為常見。過去數十年來，我國亦先後實施獎勵投資條例與促進產業升級條例等措施，給予投資者多項租稅減免以提升投資意願。然而，政府租稅獎勵措施對經濟體系造成之干擾，其整體經濟效果究竟如何？此一重要議題，無論在經濟理論或實證研究上仍然未有定論。尤其是，國內相關實證研究仍不多見。 　本研究之目的，在於使用可計算一般均衡分析法(computable general equili-brium approach)，探討近年我國獎勵投資政策中租稅減免措施的經濟效果。雖然租稅獎勵措施通常是針對特定目標產業或特定功能別活動實行，但其影響則可能透過產業間的關聯效果而對整體經濟造成衝擊，因此有必要採用一個能兼顧直接效果與間接效果的一般均衡分析方法。本研究在模型設計與資料處理上著重於營利事業所得稅稅率變動對於廠商決策影響的機制。 　本研究共進行兩個模擬。第一部份為所得稅稅率齊一化，其目的為探討因各產業間稅率不同對於資源配置效率的影響。就結果而言，實質國內產出上升0.02%。因此，在社會整體稅賦負擔不變之下，藉由所得稅稅率齊一化的作法，可以改善資源配置的效率，而使得社會總產出上升。 　第二部分的模擬為調整電子單一產業優惠幅度，其目的在評估政府給予特定產業租稅優惠的整體經濟效益。結果發現：提升受優惠之電子業的稅率10%與20%，將分別造成實質國內產出下降0.01%與0.02%。這顯示了在經濟體系內尚存在其他市場扭曲的情況下，單獨減少一個產業的扭曲程度並不會造成整體經濟效率的提升。同時，此結果也隱含我國投資獎勵租稅減免的措施確實有吸引資本進入被獎勵產業與增加總產出的效果存在，惟其程度似乎十分有限。 / Providing investors with tax benefits is widely used as an investment promoting policy tool around the world. Similar measures have been taken in Taiwan in the past years to promote investment will. What the overall economic effect of the policy is, considering the fact that such measures may be sources of distortions in the economy would be an important question. The issue is still under debate both theoretically and empirically. In addition, relative empirical studies are rare in Taiwan. The purpose of the study would be using computable general equilibrium approach to evaluate the economic effect of tax reductions in Taiwanese investment promoting policies. Although such measures are implemented upon specific industries or functions, the impact would be economy wide through interaction effects. Thus, a method being able to handle both direct and indirect effects would be necessary. The mechanism how changes in corporate income tax rate may affect decisions of firms is especially emphasized upon the design of empirical model and the processing of data. Two simulations are contained in the study. The first would be the harmonization of income tax rate, so as to evaluate the effect on allocation efficiency caused by differential corporate income tax rates among industries. The result shows a 0.02% increase in GDP. Therefore, overall tax burden being fixed, the resource allocation efficiency can be improved by harmonizing corporate income tax rate, and the output would increase. The second simulation explores possible consequences of adjusting tax benefits on electronic industry so as to estimate overall economic effects from tax advantages of investment promoting policies. The result show 10% and 20% increase in tax rates of the industry cause GDP to decrease 0.01 and 0.02 respectively. The figures may imply that Taiwanese investment promoting policy does attract capital into the encouraged industry and increase total output. The magnitude, however, does not seem to be significant.

本篇論文的目的在探討不完全競爭情況下之最適關稅理論。首次說明不完全競爭與國 貿理論及政策之關係，並介紹最適關稅理論之發展。在本文之第三章、第四章分別討 論產品市場不完全競爭，要素市場不完全競爭與最適關稅理論之關係。在最後的結果 中，發現最適關稅稅率將受到外國進口需求彈性、本國出口供給彈性、國內不完全競 爭情況及所得分配因素的影響，此一結果擴充了傳統最適關稅理論的討論範圍。