  An effective monopole action is derived from vacuum configurations after
abelian projection in the maximally abelian gauge in $SU(2)$ QCD. Entropy
dominance over energy of monopole loops is seen on the renormalized lattice
with the spacing $b>b_c\simeq 5.2\times10^{-3} \Lambda_L^{-1}$ when the
physical volume of the system is large enough. QCD confinement may be
interpreted as the (dual) Meissner effect due to the monopole condensation.
