  The relation between the angular diameter distance and redshift in a
spherically symmetric dust-shell universe is studied. We have discovered that
the relation agrees with that of an appropriate Friedmann-Lemaitre (FL) model
if we set a ``homogeneous'' expansion law and a ``homogeneous'' averaged
density field. This will support the averaging hypothesis that a universe looks
like a FL model in spite of small-scale fluctuations of density field, if its
averaged density field is homogeneous on large scales. We also study the
connection of the proper mass of a shell with the mass of gravitationally bound
objects. Combining this with the results of the distance-redshift relation, we
discuss an impact of the local inhomogeneities on determination of the
cosmological parameters through the observation of the locally inhomogeneous
universe.
