  We introduce a new index of the leptonic CP phase dependence $I_{\rm CP}$ and
derive the maximal condition for this index in a simple and general form.
$I_{\rm CP}\simeq 100%$ may be realized even in the JPARC experiment. In the
case that the 1-3 mixing angle can be observed in the next generation reactor
experiments, namely $\sin^2 2\theta_{13}>0.01$, and nevertheless $\nu_e$
appearance signal cannot be observed in the JPARC experiment, we conclude that
the CP phase $\delta$ becomes a value around $135^{\circ}$ $(45^{\circ})$ for
$\Delta m^2_{31}>0$ $(\Delta m^2_{31}<0)$ without depending the uncertainties
of solar and atmospheric parameters.
