雖然習慣不能當做刑事法律之法源，但習慣卻常常影響了刑事法律規定之犯罪構成要件。因此，在刑事法規之領域裡，不能忽視習慣之存在。本文從社會上普遍存在之各種習慣，以及實務上案例觀察，發現在刑事司法實務上面對習慣問題時，並沒有一套完整原則，致相類案件卻出現不同結果。因此，本文對習慣影響刑事法律之問題做廣泛討論，並檢討司法實務上之做法，最後試圖找出習慣與超法定阻卻違法事由之關係，做為各界之參考。

Although customs can't be the source of criminal law to criminalize or inculpate, they still often affect the constituent elements of crime. Therefore, in the field of criminal law, the existence of customs can't be ignored. In this article, we try to discover, from the practical case, that judicial decisions have no complete principles when facing customs that leads to different results in the end. Thus, through broadly discussions on customs in criminal law, and review the judicial practices, we try to find out the relationship between customs and justification for criminal offenses beyond statute and provide a guideline for public references.