The author proposes and defines “the figure of merit of fusion reactor” F which can indicate the economics of fusion reactor comparatively simply and easily by using every important evaluation factor.  An attempt to express it synthetically in a numerical formula as to magnetic confined fusion reactor is made.  By means of this evaluation formula F, some evaluation studies are carried out for each type of conceptually designed commercial reactors whose design data have been reported. The result is that Heliotron is the best, Tokamak the second, and Tandem Mirror the third.