  We investigate the impact of electroweak (EW), scalar and QCD corrections to
the full set of decay branching ratios of an additional CP-even Higgs boson
($H$) in the two Higgs doublet model with a softly broken $Z_2$ symmetry. We
employ the improved gauge independent on-shell scheme in the renormalized
vertices. We particularly focus on the scenario near the alignment limit in
which couplings of the discovered 125 GeV Higgs boson ($h$) coincide with those
of the standard model while the $Hhh$ coupling vanishes at tree level. The
renormalized decay rate for $H\to hh$ can significantly be changed from the
prediction at tree level due to non-decoupling loop effects of additional Higgs
bosons, even in the near alignment case. We find that the radiative corrections
to the branching ratio of $H\to hh$ can be a few ten percent level in the case
with the masses of additional Higgs bosons being degenerate under the
constraints of perturbative unitarity, vacuum stability and the EW precision
data. Further sizable corrections can be obtained for the case with a mass
difference among the additional Higgs bosons.
