作者
崔曉倩^* (國立中正大學經濟學系)
楊韋信 (國立中正大學國際經濟研究所)

Authors
Hsiao-Chien Tsui^* (Department of Economics, National Chung Cheng University)
Wei-Xin Yang (Institute of International Economics, National Chung Cheng University)

中文摘要
為了維持市場上一定的競爭程度，各國反托拉斯相關政策多 以市佔率做為合併門檻。本文主旨，便是嘗試由社會福利的角度， 重新檢視水平合併對於市場所形成的影響，並藉此引伸探究當市 場競爭型態不同之際，以市佔率做為規範合併基準是否毫無罅漏 之處。經由分別處理 Cournot 競爭與 Stackelberg 競爭下水平合併 對於社會福利所造成之影響後發現，市場集中度與社會福利之間的關係，會因為市場的競爭型態以及合併後的成本降幅而呈現不 同的方向。是以，相關政策於執行之際若不考慮廠商所處的競爭 型態而單以市佔率進行規範，易導致集中度愈高則社會福利水準愈低等主觀偏頗，反而妨礙有效率的合併行為。

Abstract
In order to maintain the competitive effects, horizontal mergers that are often perceived as antitrust have been regulated for an index in market share. Following the perspective of social welfare, this study is to examine the relationship between horizontal mergers and competitive effects by taking the market structure into account, and to examine whether market share is adequate for a regulation index of horizontal mergers. This study employs the market structure of the Cournot and Stackelberg models to test the effects of market concentration on social welfare when a horizontal merger takes place. The findings reveal that the competitive effects on horizontal mergers depend on the costs down due to merger and the market structures as well. Viewed in this light, the level of market share and the change in concentration resulting from a horizontal merger affect a merger's evaluation of competitiveness, and accordingly it is insufficient to regulate horizontal mergers by the index of market share.

中文關鍵字
水平合併；社會福利；市場佔有率；規範基準

Keywords
Horizontal Merger; Social Welfare; Market Share; Regulation