Shinji Miyadai (宮台真司, Miyadai Shinji, born 3 March 1959 in Sendai, Japan) is a Japanese sociologist and professor at Tokyo Metropolitan University.

He has a PhD from the University of Tokyo 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.