This paper is verifying of the effects on the electric power deregulation in Japan to the productivity of each electric power company by using the parametric and nonparametric test of the DEA (Data Envelopment Analysis) and the Inverted DEA (Inverted Data Envelopment Analysis). In this paper, the first step of the evaluation of the relative efficiencies and inefficiencies of each electric power company for a total of 21 years before and after electric power deregulation. The second step of the verification of the effects on the electric power deregulation in Japan to the productivity of each electric power company by using the parametric and nonparametric test of the DEA and the Inverted DEA are clarified. The verification of the effects on the electric power deregulation of the productivity of each electric power company was identified statistically
