The author's primary academic fields are industrial location theory, spatial economics, and regional economics. The author has made some interesting theoretical discoveries in the above academic realms. Many academic results have been presented at ERSA and the papers have been published in international journals and books: In the field of the market area theory, only regular hexagonal market area had been regarded as optimal shape, but his paper showed that equilateral triangle and square can be also optimal shape. And the author showed, using the concepts of contact price and conjectural price valuation, that the market area of retail management changes differently due to the decrease in freight rate, and the pattern of the change differs depending on department stores, supermarkets, and convenience stores. It also clarifies in his book that city systems are polarized by the decreasing freight rate.