This paper aims to examine if the controls over the ruling bureaucrats, by the ruling forces including the president, could be the core determining factor for their policy achievements, through a comparative study on the policy-making process of the Kim Dae-Joong and Roh Mu-hyun administration. Moreover, this provides new factors which can contribute to the effective controls over bureaucrats, criticizing that the existing discussions about the policies towards North Korea have focused merely on the presidents` leaderships or have superficially described the interaction between presidents and bureaucrats. One of the key measure for ruling forces to effectively control bureaucrats is a ‘powerful mediator.’ In fact, the trade-off between the control over bureaucrats and the realization of the policy intention could be generated, depending on whether a minister gets promoted from within the ministry or selected from outside of the organization. Then, a ruling force would be encouraged to employ a ‘powerful mediator’ who can minimize those trade-off and connects itself harmoniously with bureaucrats. if it holds the resources for the employment. This is because the appropriate employment of ‘powerful mediators’ can help a ruling force to bring good policy performances. This paper would be meaningful in clarifying that the success of policies depends on procuring control power towards bureaucrats and in conceptualizing the new factors which compose it, especially the ‘powerful mediator.’ In particualr, besides North Korea Policy, the conflict between the political and bureaucratic power as well as a certain tension generated from the differences in the preferences of each ministries could be seen also in other policy-making arena. Hence, a ruling forces is required to secure a plenty of ‘powerful mediators,’ who are qualified with the expertise and confidence to persuade the president`s policy stance to bureaucrats and correspondingly induce them to implement even the reform against their own interests.