  Degeneracies of the neutrino oscillation parameters are explained using the
$\sin^22\theta_{13}$--$s^2_{23}$ plane. Measurements of $\sin^22\theta_{13}$ by
reactor experiments are free from the parameter degeneracies which occur in
accelerator appearance experiments, and reactor experiments play a role
complementary to accelerator experiments. It is shown that the reactor
measurement may be able to resolve the degeneracy in $\theta_{23}$ if
$\sin^22\theta_{13}$ and $\cos^22\theta_{23}$ are relatively large.
