  We study the relation between the instanton distribution and the monopole
loop length in the SU(2) gauge theory with the abelian gauge fixing. We measure
the monopole current from the multi-instanton ensemble on the $16^4$ lattice
using the maximally abelian gauge. When the instanton density is dilute, there
appear only small monopole loops. On the other hand, in the dense case, there
appears one very long monopole loop, 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.
