Japan's policy of “public understanding of science” (PUS) has shifted to “science communication” since 2003. That year, there were a number of simultaneous developments with regard to science communication. The key report that advocated for the promotion of science communication and a textbook on science communication were published then. The most important consequence was that the report triggered a policy change at the Ministry of Education, Culture, Sports, Science and Technology (MEXT). The following year, MEXT published the White Paper on Science and Technology 2004, the main theme of which was concerned with science communication. Although the shift may have begun as a somewhat top-down contrivance, it has subsequently sunk down firm roots throughout Japan. In 2011 the Japanese Association for Science Communication was founded. People's awareness of science communication was significantly changed by the Great East Japan Earthquake that occurred on March 11, 2011. Why was such a policy shift possible? How did such a cascade effect occur? This paper will discuss the reasons behind these phenomena.