Effects of charged Higgs boson and QCD corrections in $\bar B \to D \tau \bar\nu_{\tau}$

We study effects of charged Higgs boson exchange in $\bar B \to D \tau \bar\nu_{\tau}$. The Yukawa couplings of Model II of two-Higgs-doublet model, which has the same Yukawa couplings as MSSM, is considered. We evaluate the decay rate including next-to-leading QCD corrections and estimate uncertainties in the theoretical calculation. Our analysis will contribute to probe an extended Higgs sector at B factory experiments.