證券交易法明文禁止內線交易，內部人若知悉重大影響股票價格之消息（下稱重大消息），在消息未公開或公開後十八小時內買賣公司股票者，即構成內線交易。以時間序而言，重大消息成立後至公開後十八小時內，知悉消息之內部人不得合法買賣股票，但何時重大消息成立、何時公開，卻未有明文規定，僅能依個案事實綜合判斷之，而如此不免產生認定爭議。惟內線交易行為人需受嚴厲之刑事處罰，對於構成要件宜明確並足供行為人預測其行為結果，較為妥當，故對於重大消息成立與公開時點之判斷，實有必要建立較為具體的標準。而國內對於「重大消息成立」此問題已有相當多討論，但對「重大消息公開」之學術研究相對有限，故本文擬以後者為題，從近期司法實務對此議題之分歧意見出發，嘗試以美國法觀點對我國現行制度加以分析與檢討，並提出具體建議，以期能更完善我國內線交易之規範。

Under the Securities and Exchange Act (the SEA), insiders knowing material non-public information relating to a particular stock should refrain from trading such stock unless they wait 18 hours after the information becomes public. However, the SEA does not have any definitions of public/non-public information and whether the material information at issue is public or non-public tends to be an open question in some cases. Insider trading is a felony that would severely punish violators and thus all the elements of the felony, including material non-public information, should be reasonably predictable, but the SEA fails to do so. It seems worse that courts so far have had different points of view in this regard. This article suggests that the SEA consider providing more clear criteria to determine when material non-public information becomes public. This article is expected to have a comparative law study with the U.S. and to offer a proposal to reform the existing regulations with respect to insider trading.