The timing criteria for determining the acquisition of distinctiveness by the use of a trademark that is not inherently distinctive can be classified into the criterion of the time of an application, the time of decision for registration, the time of trial decision, or the time of closing arguments in a court trial. It has been recognized as the time of decision for registration by precedents and theories amid ambiguous regulations under the Trademark Act. However, the Supreme Court's 2011Hu3698 en banc decision of the trial to confirm scope of rights on March 20, 2014 ruled the time of trial decision as the reference point as to whether the mark had acquired distinctiveness and changed its previous position of the time to decide whether to register. In particular, this ruling is significant in that a degree of distinctiveness of the trademark acquired by the use was recognized as of the time of trial decision in the trial to confirm scope of rights even though this trial is about the distinctiveness acquired by the use after registration. Discussions have been divided over the meaning of the above ruling, such as criticizing it as a ruling against the first-to-file rule under trademark law and saying that recognition of such distinctiveness is not a problem because it is only for the judgment of similarity between trademarks, but failed to reach a consensus conclusion. In this paper, if the Korean Trademark Act has a trial system for confirming scope of rights despite recent discussions on the abolition of it, the meaning of the trial decision can be interpreted more actively and even defects in a registered trademark with a reason for invalidity due to lack of distinctiveness in the entire trademark at the time of decision for registration, provided that the IPTAB confirmed the acquisition of distinctiveness ‘at the time of trial decision’, could be corrected. The reason for this is that ‘whether distinctiveness of a trademark is acquired’ is about the requirements for trademark registration, ‘the judgment authority of which the KIPO has exclusively’, and the IPTAB's decision in the scope of rights confirmation trial is a quasi-judicial administrative act of ‘an institution authorized by law’, having irrevocable power with authentication and, ‘for matters related to the KIPO’s exclusive authority from the decision’, the ‘formative effect’, changing the existing administrative act. The concept of ‘distinctiveness’ itself is bound to be very fluid in response to changes in consumer perceptions in the market, and the trademark protection system as a whole, including related contents of the Unfair Competition Prevention Act, takes the public interest, such as market order and consumer interests, as the most important protection targets, unlike the patent system that protects the result of one’s creation. Thus, the timing criteria for determining the scope of rights in the scope of rights confirmation trial should also be set from this point of view, and it would be a good way to ensure that the current market situation is well reflected. It is ideal to follow the first-to-use rule of the trademark protection law, except for administrative convenience factors. The Trademark Act already considers the ‘extinction’ of distinctiveness, a requirement for trademark registration, after registration, as a later occurring reason for a invalidation trial in Article 117 (1) 6 of the Trademark Act, and, in this context, the ‘occurrence’ of distinctiveness after registration can also be recognized through a trial to confirm scope of rights. It can be seen that the Trademark Act has regulations based on the first-to-use rule even after registration to carry out specific judgments on the existence of distinctiveness at the present time.