  Recent studies of confinement based on the idea of abelian monopole
condensation are reviewed briefly. Emphasis is placed on the approach to get
the effective monoole action using the blockspin transformation on the dual
lattice. The trajectory obtained looks to be the renormalized one in $SU(2)$
QCD. A disorder parameter of confinement is constructed. Monopole condensation
occurs also in $SU(3)$ QCD.
