  The spin of the $\tau$ lepton in the semiletonic process
${\bar{B}}^0\rightarrow D^{+} \tau^- {\bar{\nu}}$ can be polarized in the
direction which is normal to the reaction plane, if the charged Higgs boson
exists and its coupling to quarks has a complex phase. We calculate this
transverse polarization of the $\tau$ lepton by using the experimentally
measured $B$ to $D$ transition form factors.
