  We derive the effective action of the light fermion field of the domain-wall
fermion, which is referred as $q(x)$ by Furman and Shamir. The inverse of the
effective Dirac operator turns out to be identical to the inverse of the
truncated overlap Dirac operator, except a local contact term which would give
the chiral symmetry breaking in the Ginsparg-Wilson relation. This result
allows us to relate the light fermion field and the fermion field described by
the truncated overlap Dirac operator and to understand the chiral property of
the light fermion through the exact chiral symmetry based on the
Ginsparg-Wilson relation.
