  The production process of the charged Higgs-boson associated with a $W$ boson
at electron-positron colliders is discussed in the two-Higgs-Doublet Model
(2HDM) and in the Minimal Supersymmetric Standard Model (MSSM). The process is
induced at one-loop level in these models. We examine how much the cross
section can be enhanced by quark- and Higgs-loop effects. In the non-SUSY 2HDM,
in addition to large top-bottom ($t$-$b$) loop effects for small $\tan \beta$
($\ll \sqrt{m_t/m_b}$), the Higgs-loop diagrams can contribute to the cross
section to some extent for moderate $\tan \beta$ values. For larger $\tan
\beta$ ($\gg \sqrt{m_t/m_b}$), such enhancement by the Higgs non-decoupling
effects is bounded by the requirement for validity of perturbation theory. In
the MSSM with heavy super-partner particles, only the $t$-$b$ loops enhance the
cross section while Higgs-loop effects are very small.
