A copyright system is designed to produce more developed cultural environment that nurtures author`s creation and user`s enjoyment of works, according to Article 1 of Korean Copyright Law. To achieve the ultimate goal, criminal copyright law should not be easily applied to individuals who lack intent to infringe because it is regarded as a crucial element of willfulness to constitute criminal copyright infringement, while knowledge of illegality has been considered as a separate element from willfulness by majority of legal scholars. However, due to its complexity comprising technical statutes and applicability to the public at large, copyright law has the trait to be treated differently: knowledge of illegality as a constituent part of willfulness. In this article, I argue that applying theory of intent can be one way to perform the policy of copyright law by introducing US`s Moran case. Here, the court used subjective standard when interpreting willfulness, meaning the defendant`s good-faith belief that he was not violating any provisions of the Copyright Act should be the standard even if it looks unreasonable by an objective judgment. Moreover, once the reasoning that knowledge of illegality is entwined with intent to infringe in the realm of copyright law is accepted, ignorance of the law should not be discriminated from other mistake of law defense.