股票購回計畫提供公司向市場傳達自評價值態度的管道。然而，一般投資人難以辨認公司宣稱本身價值訊號的真偽，故購回計畫可能潛伏操弄股價的意圖。本研究以購回計畫中揭露的訂價水準，區別出公司自認為存在較嚴重低估問題的樣本。實證結果顯示，針對自評價值過於樂觀的公司，具有三個特徵指向其安排購回計畫動機傾向為干擾市場。首先，實際購回股份結果與計畫內容差異較大。其次，回顧宣告計畫前，並未偵測到可具體支持價值被低估的證據。最後，宣告績效較佳，亦即公司自評價值訊息會促使市場產生相對應的調整，但是該表現卻僅侷限於預定執行期間。

Share repurchase plan (SRP) provides an opportunity for the firms who try to convey their own self-evaluation attitude about the intrinsic value. However, identify the signal is a difficult task for uninformed investors, thus SRP may hide the manipulation purpose of firms. This paper investigates how the firms interfere in stock market by arranging SRP, and observes the samples that unilateral revealed existence of serious undervalued problems. The empirical results show that the firms with overoptimistic self-evaluation have three distinct features in SRP event. First, the outcomes of executing share buyback would be far from the program. Second, reviewing the theoretical return before announcement period, it detected no specific evidence to demonstrate the existence of undervalued problem. Finally, the per-formance could beat the benchmark, and consequently the market valuation would be adjusted in terms of the signal that SRP revealed. But the achievement was limited to the predetermined execution period only.