  The decay rate of a (neutral) Higgs boson ($H$) going into a longitudinal
$W$-boson pair is calculated by including one loop radiative corrections in a
two-Higgs doublet model. It is assumed that the
  Higgs boson $H$ is much heavier than the $W$ boson and a full use has been
made of the equivalence theorem. A possibility is explored extensively that the
precise measurement of the decay rate of $H$ could be useful as a probe of the
other neutral as well as charged Higgs bosons through potentially important
radiative corrections. It is pointed out that, for some choice of the
parameters, the radiative corrections are sizable and that there exist a
possibility of extracting useful information on the other Higgs boson masses.
