The classic conception of public opinion was fonned in modern "civil society." In present day society，however，public opinion became incapable of adapting itself to such classic conception. Grasping the public opinion as system-functional conception，N. Luhmann intends，to understand and clear the function of public opinion in the complicated present-day political and social systems as "thmatising" one. In this paper，thesis of N. Luhmann is examined to evaluate its propriety.