  We study the confinement physics in QCD in the maximally abelian (MA) gauge
using the SU(2) lattice QCD. To clarify the origin of abelian dominance for the
long-range physics, we study the charged-gluon propagator in the lattice QCD,
and find that the effective mass $m_{ch} \simeq 0.9 {\rm GeV}$ of the charged
gluon is induced by the MA gauge fixing. In the MA gauge, there appears the
global network of the monopole world-line covering the whole system, which
would be identified as monopole condensation at a large scale. To prove
monopole condensation, we apply the dual gauge formalism to the monopole part,
and derive the inter-monopole potential from the dual Wilson loop in the MA
gauge. In the monopole part, which carries the nonperturbative aspects of QCD,
the dual gluon mass is evaluated as $m_B \simeq $0.5GeV, which is the evidence
of the dual Higgs mechanism by monopole condensation. As for the monopole
structure, the large fluctuation of off-diagonal gluons remains around the
monopole in the MA gauge, and large cancellation occurs between the diagonal
and off-diagonal action densities to keep the total QCD action finite. The
charged-gluon rich region around the QCD-monopole would provide the effective
monopole size as the critical scale of the abelian projected QCD. Instantons
are expected to appear in the charged-gluon rich region around the monopole
world-line in the MA gauge, which leads to the local correlation between
monopoles and instantons.
