In the filed of negligent co-perpetration(NCP), highligts the legal indeterminacy. For so many legal reasons conflict between the affirmative and the negative of NCP. In Korea as well as Germany and Japan, the negative of NCP is dominant position of legal academy, but the supreme Court of Korea and Japan affirm NCP differently from German Court. This essay examines legal reasons of the affirmative and negative in turn and establish that the affirmative is more persuasive and successful than the negative as a interpretation of Art.30 of Korean Penal Code. Main argument of this essay is that the structures of intentional and the negligent perpetration are different, therefore the standards of co-perpetration are also different. From this premise, the NCP could be formed without co-determination of commission(CDC), because CDC is a peculiar element to intentional co-perpetration(ICP). The legal reasons of negative position of NCP could not defend against this argument. So this essay conclude that NCP is legally justified by the criminal dogmatics. In addition to theoretical justification of NCP, practical reasons support the affirmation of NCP. Today, the more our society develops and divides into specialized parts, the more fields of our life request us to work together, that is, cooperate with other people. Taken this phenomena into account, the NCP theory can protect our society from the danger that one could be easily excused from vilotation of common duty defending himself by his belief that other people will abide by the common duty even if he neglect the duty. In short, the practical value of NCP is the prevention of ‘Organized Irresponsibility’, that is, shirking of his responsibility under cover of organization.