Four Composers, La Monte-Young, Terry Riley, Steve Reich and Philip Glass, who represent American Minimalist Music in the 1960's, experimented various repetitive musical forms in their unique ways. Young focused on the unique difference of a note (or two notes) produced by the repetitive patterns of overtones in the sustained sound, and Riley produced an infinite multiplicity through the repetition of the definite given modules. Reich experimented musical repetitive forms by his own ways called 'Phase Shifting Process', and Glass made his unique repetitive forms by adding and subtracting some notes sequentially to the given pattern. They made the repetitive forms altogether in their ways. But the important thing lies not in the fact that all of them experimented the repetitive musical forms, but in the radical meaning their repetitive forms imply. We can find the fundamental significance of their repetitive forms in the radical changes of musical thought they caused. In the traditional music the repetitive forms functioned as a mechanism which enabled the musical ideas (motives or themes) to be recognized by the transformative repetitions. But in the minimalist music the repetitive forms function as a mechanism producing differences. The radical characteristics of minimalist repetition can be explained by applying Deleuze's concept of difference. Deleuze contrasted difference with generality and identity, therefore brought the new meaning of repetition into the light. His concept of difference leads to the denial of so called 'representationalism'. The representinalism in the music means that musical works realize the consistent ideas or themes. In this case a musical work is regarded as a medium to recognize the grand narrative in it, and finally disapproved of every moment's own value. The radical characteristic of Minimalist Musical thought can be found in the fact that they tried to overcome the negative results of musical representationalism by experimenting various repetitive musical forms.