  We calculate renormalized Higgs boson couplings with gauge bosons and
fermions at the one-loop level in the model with an additional isospin singlet
real scalar field. These coupling constants can deviate from the predictions in
the standard model due to tree-level mixing effects and one-loop contributions
of the extra neutral scalar boson. We investigate how they can be significant
under the theoretical constraints from perturbative unitarity and vacuum
stability and also the condition of avoiding the wrong vacuum. Furthermore,
comparing with the predictions in the Type I two Higgs doublet model, we
numerically demonstrate how the singlet extension model can be distinguished
and identified by using precision measurements of the Higgs boson couplings at
future collider experiments.
