We study the relation between the instanton distribution and the monop
ole loop length in the SU(2) gauge theory with the abelian gauge fixin
g. The measure the monopole current from the multi-instanton ensemble
on the 16(4) lattice using the maximally abelian gauge. When the insta
nton density is dilute, there appear only small monopole loops. On the
other hand, in the dense case, there appears one very long monopole l
oop, which is responsible for the confinement property, in each gauge
configuration. We find a clear monopole clustering in the histogram of
the monopole loop length from 240 gauge configurations.