North Korea has actually possessed nuclear weapons, whereas Iran has remained in the developmental stage of its nuclear-weapon program. A large literature has analyzed these nuclear issues, but has rarely compared them. However, comparing these nuclear cases is helpful to find policies to resolve the North Korean nuclear issue by revealing factors that cause the different statuses of their nuclear-weapon programs. Thus, we compare their nuclear-weapon programs with two concepts: nuclear opportunity, conditions needed to initiate and maintain nuclear programs, and nuclear willingness, factors leading to a state’s eagerness to possess nuclear weapons. This analysis reveals that North Korean and Iranian different international insecurity conditions and domestic political structures have caused their different levels of nuclear willingness and thus the different statuses of their nuclear-weapon programs. However, they have the similar level of nuclear opportunity. We suggest three policies to denuclearize the Korean Peninsula based on this analysis.