Maruyama Masao （1914 - 1996） famously expressed his political thought by "democracy as permanent revolution" in the addition to the third part of his book Thought and Behavior in Modern Japanese Politics（enlarged edition, 1964）. Also, Maruyama made his "bet on the sham of postwar democracy" in the postscript of the same book. This article traces his thought of democracy during the postwar period and considers his idea of democracy as permanent revolution. After the end of World War II, Maruyama worried about democracy for more than a half year partly due to his skepticism about its contradictions. With the announcement of the drafted constitution in March 1946 , he converted to the principle of the sovereignty of the people, and wrote about the so-called democratic revolution of Japan. Since 1949 he was committed to the movement of the democratic camp, pursuing democratization of Japanese society and protesting against the conservative and reactionary forces. Around 1960 he talked about the paradox of democracy, for the government of the people was not natural as Rousseau thought. Shortly after the rise of the Anti-Anpo movement, he wrote in his notebook that not socialism, but democracy deserved the name of "permanent revolution" because of the paradox of the government of the people. Democracy had been the protest concept against the orthodox concept for Maruyama until 1960 . In 1964 , when he professed democracy as "permanent revolution," he kept such literary radicals in his mind as Tanigawa Gan, Yoshimoto Takaaki and their epigones. His idea of democracy as "permanent revolution" was to routinize the revolution as the process of everyday movement. Since then, he had never mentioned "democracy as permanent revolution" before the late 1980 s. Exceptionally, he disputed with students about "permanent revolution" of Trotsky at the University of Tokyo Struggles in 1969 .