Majorana neutrinos are postulated in both theories of neutrinoless double beta decay (0nuBB) and seesaw mechanism. The observation of 0nuBB would be an evidence of the seesaw mechanism, and support the Leptogenesis scenario of early universe. The DCBA experiment measures kinetic energy of individual beta ray in 0nuBB with powerful background rejection capability. A prototype called DCBA-T2 is in the engineering operation, and another one DCBA-T3 with better energy resolution is under construction. For the future project, MTD is designed on the basis of DCBA-T2 and T3 in order to study the absolute mass scale of Majorana neutrino down to 0.05 eV.