Japan started a political reconstruction project at 1990s and now has accomplished two reforms: One is ''electoral system reform”, which consolidates the party president's political power; and the other is ''administrative reform”, which strengthens Japan prime minister's political authority. After holding the LDP's presidential position and forming a cabinet, Koizumi thoroughly utilized the authority that political reconstruction project granted. He weakened the influences of factions and rectified the policy-making pattern. Consequently, ''Koizumi Regime'' becomes the focus of modern Japan politics researches, and the promotion of postal privatization bill is an absorbing case. The aim of this paper is to analyze the transformations of policy-making pattern from the process of postal privatization bill promoted by Prime Minister Koizumi.