  We reanalyze the proton decay in the minimal SU(5) SUGRA GUT model. Unlike
previous analyses, we take into account a Higgsino dressing diagram of
dimension 5 operator with right-handed matter fields ($RRRR$ operator). It is
shown that this diagram gives a dominant contribution for $p\to
K^+\bar{\nu}_\tau$ over that from $LLLL$ operator, and decay rate of this mode
can be comparable with that of $p\to K^+\bar{\nu}_\mu$ which is dominated by
the $LLLL$ contribution. It is found that we cannot reduce both the decay rate
of $p\to K^+\bar{\nu}_\tau$ and that of $p\to K^+\bar{\nu}_\mu$ simultaneously
by adjusting relative phases between Yukawa couplings at colored Higgs
interactions. Constraints on the colored Higgs mass $M_C$ and a typical squark
and slepton mass $m_{\tilde{f}}$ from Super-Kamiokande limit become
considerably stronger due to the Higgsino dressing diagram of the $RRRR$
operator: $M_C > 6.5 \times 10^{16}\gev$ for $m_{\tilde{f}} < 1 \tev$, and
$m_{\tilde{f}} > 2.5 \tev$ for $M_C < 2.5 \times 10^{16} \gev$.
