  Several different effects in electroweak quantum corrections are explored
separately through the latest data on the weak-boson masses. The leading-log
approximation, the improved-Born approximation and the non-decoupling top-quark
effects are studied without depending on the recent CDF data of $m_t$, and the
results are given in a form independent of the Higgs mass. On the other hand,
the bosonic- and the non-decoupling Higgs effects are examined by fully taking
account of those CDF data. It is emphasized that future precision measurements
of $M_W$ and $m_t$ are considerably significant not only for further studies of
the electroweak theory at higher confidence level but also for new physics
searches beyond it.
