Though the suspect is under no specific suspicion, one will be arrested by an investigation agency. Seemingly illegal, however, it is permitted to do the urgent arrest only if the suspect will be released with the agency winning the written permission and report of a prosecutor, under the current criminal procedural law. The urgent arrest could be preferred and overused because generally the investigation agency places major emphasis on promptness and efficiency in investigating. In the case, a question of human rights infringement might be raised. This article focuses on reviewing on the problem of urgent arrest as mentioned above and submitting as reasonable improvement plans as follows; First, it is required to introduce ex facto custody warrant system if we intend to maintain current urgent arrest system to control the situation after urgent arrest. This makes it possible to fulfill constitutional warrant-requirement principle thoroughly in order to guarantee human rights and prevent the abuse of the investigation power. Secondly, under the current law, after the urgent arrest, a prosecutor should request an arrest warrant for the suspect 'without delay', and the period of claim is within 48 hours. However unlike general arrest, it would be required to investigate with promptness in emergency arrest. So, for the period of claim, 36 hours will be reasonable I think. Third, in urgent arrest, the investigation agency should immediately request a prosecutor to issue an arrest warrant. But this kind of procedure could be against the Constitution`s principle of the division of power. In order to utterly guarantee human rights, it will be more appropriate to abolish the system of a prosecutor's approval and to introduce the system of judiciary approval. With these notions, I suggest that the judicial police directly request an arrest warrant to a judge. It will be necessary to revise a prosecutor's exclusive right to request an warrant. Fourth, under the current Criminal Procedure, the urgent arrest system is similar to the urgent confinement system in the past, and it could violate the principle of the fundamental rights in the Constitution. Therefore, it would be better to employ the terminology of the urgent confinement system rather than urgent arrest system. Fifth, in respect to construing current law, from the standpoint of protecting the suspect's rights, it should be considered not to admit additionally examining a suspect by requesting a warrant after being urgently arrested. However, if the suspect is urgently arrested and taken over to a judge under approval of arrest, additional examination could be permitted. The same holds true of a simple filling out an arrest form or doing another excuse for the prompt investigation. Conclusively, the system of urgent arrest could be applied more legitimately and effectively in supplementing ex post facto custody warrant. Considering improper use of urgent arrest power by investigative authorities, the characteristic of the urgent arrest would be interpreted in the middle of-the-road-policy between arresting and detention.