Anand M. Goel and Anjan V Thakor 於最近的財務學刊中提出理性且風險趨避的經理人會放棄部分正報酬但風險高的投資，造成投資不足問題，使得公司價值未能極大化。然而，極端過度自信的經理人投資正負報酬皆有的計畫，造成過度投資，使得公司價值遞減。只有中度自信的經理人能為公司價值帶來極大化效果。本篇研究採用台灣上市櫃公司近二十年資料，以公司經理人對公司持股的變化來衡量其過度自信的程度，探討公司經理人自信程度對公司獲利能力與公司價值的影響。實證研究發現，極端過度自信的經理人與極端保守的經理人使公司的績效與成長性減少，降低公司價值。此研究增加我們了解經理人自有特徵對公司價值的影響，並為公司理財課題帶來新的貢獻。 / Former literature theorized that excessively overconfident CEOs and excessively diffident CEOs reduce the firm value for underinvestment and overinvestment problems and moderate overconfident CEOs willing to take risky but positive NPV projects increase the firm value. This paper conducts an empirical research by using the change of purchase and sale on own company stocks took by CEOs to measure CEO overconfidence level in Taiwanese listing companies and find that the profitability and stock performance of firms led by excessively overconfident CEOs and excessively diffident CEOs decrease compared to by moderate overconfident CEOs. The result contributes to the understanding of the impact on firm valuation by CEO idiosyncratic characteristics and offers new evidence to behavior finance on corporate management.