本論文嘗試分析一個同質雙佔市場，在負的外部成本存在下，政府對廠商課徵皮古稅後，對廠商技術選擇的影響。本文引用Roller和Tombak(1990)的模型並加以改良，分析加入皮古稅後，所得出的結果是否有所改變。其中將相關決策者之行為及其間之互動建構成一個同質雙佔市場之三階段賽局:第一階段，政府設定稅率；第二階段，廠商決定是否採用高生產技術；以及第三階段，廠商進行市場Cournot競爭。
本文最後發現，如果高生產技術與低生產技術之間的邊際成本差距不夠近，就算投資高生產技術所需的固定成本很小，政府也不鼓勵廠商採取高生產技術。並且發現固定成本的不同會導致廠商所採用的策略有所不同。唯有在高生產技術與低生產技術間的邊際成本差異夠小以及高生產技術固定成本夠低的情況下，政府才會採用高生產技術的最適稅率進而誘使廠商採取高生產技術。

We construct a simple model to analyze the influences of the government imposing Pigouvian taxes on firms in a homogeneous duopoly market in which negative externalities in production exist. Roller and Tombak(1990) is the basic framework which is extended in order to take externalities and Pigouvian tax into consideration. A three-stage game is delineated to describe the behaviors of the relevant parties and their interaction: in stage one, the government decides the optimal tax rate, in stage two, the firms decide whether to adopt the high technology, and in stage three, Cournot competition.
This article finds out that if the difference in the marginal costs between high technology and low technology is not small enough, the government is not inclined to encourage the adoption of high technology even if the fix costs of high technology is small. Moreover, the fix cost of adoption the high technology is crucial. Only under the conditions that the difference in the marginal costs is sufficiently small and that the fix costs of adopting the high technology is sufficiently low, would the government set a tax rate that induces the adoption of high technology.

第一章 導論
第二章 模型
第三章 均衡策略及比較靜態分析
一、 Cournot競爭
二、 廠商技術選擇
三、 政府最適稅率
四、 不同參數下的均衡策略
第四章 結論

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