The neutral molecule, monocation, and dication of BDNT, which shows a one-step two-electron oxidation property, were characterized by a spectroscopic method. The extreme closeness of the first and second oxidation potentials is ascribable to the large structural change from BDNT1+ to BDNT2+. The on-site Coulomb energy U and transfer integral t of monoclinic BDNT-PF6 were estimated to be 0.8 eV and 0.13 eV, respectively. The coupling constants of the vibronic band were estimated by the least-squares fitting of the dimer-model function to the observed conductivity spectrum. These coupling constants shows that BDNT1+ is rather rigid compared with TTF, TCNQ, or Chloranil.