He has a Ph.D from Tokyo University for his research on Mathematical sociology. Using the method of game theory, he analyzed how the power of the state works in society. He is one of the most outspoken sociologists in Japan, and is currently working on the strategy the Japanese government should adopt for the 21st century.
He has been a constant presence in the world of Japanese letters since the publication of his PhD dissertation in 1989. His controversial work on compensated dating in Japan was the subject of much discussion after its publication.
Even though he was a great fan of Takaaki Yoshimoto, Miyadai was planning to become a natural scientist as a teenager. Students in Japan make decisions about whether they are majoring in the natural or the social sciences in university when they are in high school. Miyadai recalls that reading Abe Kobo prompted his interest to move toward social issues. Miyadai entered Tokyo University in 1978 to become a film director. He majored in sociology which he thought might be useful. Meeting Wataru Hiromatsu and Naoki Komuro made Miyadai study seriously. Reading Noam Chomsky also inspired him.