"The core of the economic problem facing us today is the concentration of power in a few hands." This was written exactly 10 years ago in Estes Kefauver's book "In a Few Hands" (1965). Needless to say, it was written about the U.S.A. However, these words have an urgent sound to Japan today. In September 1974, the Fair Trade Commission(FTC) published "The Proposed Main Points of the Antimonopoly Act Revision" (as set out in Appendix A.). Ever since, discussions centering on these proposals have become increasingly vigorous, and voices for or against them have been heard from the various related government offices, all political parties, industrial circles, consumer groups, economists and legal academics. Why then must the present Antimonopoly Law in Japan be revised and strengthened? The main purpose of this paper is to clarify some of the aspects of the economic background of this question.