Double beta (beta-beta) decays of Mo-100 were studied by means of ELEGANTS V. A finite half-life of T1/2(2v) = (1.15(-0.20)+0.30) X 10(19) yr (68% CL) for 2v-beta-beta decay and the most stringent lower limit of T1/2(0v) > 4.7 X 10(21) yr (68% CL) on the half-life for the 0v-beta-beta decay were obtained. The observed T1/2(2v) indicates very severe cancellation of the components of the relevant nuclear matrix element.