  In $\nu_{\mu} \to \nu_{\mu}$ oscillations, we find that the effect of the CP
phase $\delta$ becomes large in the region $E<2$ GeV and $L>2000$ km. In this
region, the change of the probability in this channel reaches about 0.4 due to
the CP phase effect beyond our expectation in the case of large 1-3 mixing
angle. Furthermore, the CP phase effect have almost same sign over the region
$E>0.5$ GeV so that one may find the signal of CP violation by measuring the
total rate only. As an example, we use an experimental setup and demonstrate
that the allowed region is limited to one by combined analysis of $\nu_e$ and
$\nu_{\mu}$ events although there remain three allowed regions by the analysis
of $\nu_e$ events alone.
