  We analyze which momentum component of the gluon field induces spontaneous
chiral symmetry breaking in lattice QCD. After removing the high-momentum or
low-momentum component of the gluon field, we calculate the chiral condensate
and observe the roles of these momentum components. The chiral condensate is
found to be drastically reduced by removing the zero-momentum gluon. The
reduction is about 40% of the total in our calculation condition. The
nonzero-momentum infrared gluon also has a sizable contribution to the chiral
condensate. From the Banks-Casher relation, this result reflects the nontrivial
relation between the infrared gluon and the zero-mode quark.
