本論文利用一個垂直相關市場模型，討論有一上游中間財廠商同時供應中間財給兩個不同產業的廠商時，若其中一產業的廠商有意跨足到另一產業的情況下，上游廠商的最適訂價策略，以及對社會福利的影響。我們不失一般性地令兩產業各有一家廠商A與B，其中廠商B為有意跨產業生產的廠商。本論文得到的重要結果如下。
（一）	當上游廠商採取單一訂價時，當跨業生產成本不會太高時，上游廠商會刻意降低中間財價格以增加廠商B的跨產業生產誘因。在此情況下，廠商B若跨產業生產，有可能會使上游廠商及兩家下游廠商的利潤皆提升，此外，兩產品市場的消費者剩餘以及社會福利也皆可能提高。
（二）	當上游廠商採取差別訂價時：(1)若兩產品市場規模差異不大，當跨業成本不會太高時，上游廠商會刻意降低廠商B的中間財價格，並提高廠商A的中間財價格，以增加廠商B的跨產業生產誘因。在此情況下，若廠商B跨產業生產，也有可能會使上游廠商及兩家下游廠商的利潤提升，此時，A產品市場的消費者剩餘及社會福利反而有可能因B廠商的加入而減少，反之，B產品市場的消費者剩餘則反而有可能增加。(2)若兩產品市場規模差異很大下，當跨業成本不會太高時，上游廠商會刻意提高廠商B的中間財價格，並降低廠商A的中間財價格，以降低廠商B跨產業生產的誘因。在此情況下，即使廠商B未跨產業生產，也可能使廠商B的利潤減少，而廠商A的利潤則反而可能會提高，此時，A產品市場的消費者剩餘及社會福利將會隨著跨業成本越低而提升，而B產品市場的消費者剩餘則會因而降低。

This dissertation uses a vertically-related market model to discuss when an upstream firm sells the intermediate goods to two downstream firms in different industries. Given one of the downstream firm in tend to cross industry and sell in the other market. We analyze the impacts on the upstream firm’s pricing and the social welfare. Let firm A is a downstream firm in market A and firm B in market B. Firm B is the firm intends to sell in both markets. The main findings in this dissertation are as follows.
　　First, under uniform pricing of the upstream firm a few cross-industry costs, the upstream firm will reduce the price of intermediate goods to induce firm B to sell in two markets. Given firm B decides to sell in markets, it is possible that the profits of the upstream firm, firm A, and B will increase. In addition, both markets consumer surplus and social welfare may also increase.
　　Second, under price discrimination of the upstream firm: (1) If the difference between these two markets’ size is small, and the firm B serves in both markets, the upstream firm’s and both of the downstream firms’ profits may also increase. But interestingly, the consumer surplus of market A and the social welfare may be lower when firm B serves in both markets. However, consumer surplus of market B may increase. (2) If the difference between these two markets’ size is large, even firm B serves only the market B, its’ profit may decrease, while the profit of firm A may increase. In this case, as the cross-industry cost is lower, the consumer surplus of market A and the social welfare will increase, however the consumer surplus of market B will decrease.

目　錄
第一章	   前言   ………………………………………………..1
第二章	   基本模型   ……………………………………………6
       2.1  中間財單一訂價   ………………………………….…7
       2.2  中間財差別訂價   ……………………………..…...8
第三章	   跨產業模型   ……………………………………..…10
       3.1  中間財單一訂價   …………………………………...10
       3.2  中間財差別訂價   ……………………………...…16
第四章	   福利分析   ………………………………………….29
       4.1  單一訂價   ………………………………………..….29
       4.2  差別訂價 ……………………………..………….31
第五章	   結論   ……………………………………………...36
參考文獻   ……………………………………………………………38

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