  We investigate CP-violation effect in the long-baseline neutrino oscillation
in the four-neutrino model with mass scheme of the two nearly degenerate pairs
separated with the order of 1 eV, by using the data from the solar neutrino
deficit, the atmospheric neutrino anomaly and the LSND experiments along with
the other accelerator and reactor experiments. By use of the most general
parametrization of the mixing matrix with six angles and six phases, we show
that the genuine CP-violation effect could attain as large as 0.3 for $\Delta
P(\nu_\mu\to\nu_\tau) \equiv P(\nu_\mu\to\nu_\tau) -
P(\bar{\nu_\mu}\to\bar{\nu_\tau})$ and that the matter effect is negligibly
small such as at most 0.01 for $\Delta P(\nu_\mu\to\nu_\tau)$ for $\Delta m^2 =
(1-5)\times 10^{-3} {\rm eV}^2$, which is the mass-squared difference relevant
to the long-baseline oscillation.
