  In high-Tc cuprates, the orbital magnetoresistance in plane (MR,
$\Delta\rho/\rho$) is anomalously enhanced at lower tempemeratures compared
with conventional Fermi liquids, and thus Kohler's rule is strongly violated.
Moreover, it should be noted that an intimate relation between the MR and the
Hall coefficient ($R_H$), $\Delta\rho/\rho \propto (R_H/\rho)^2$, holds well
experimentally, and is called the "modified Kohler's rule". In this letter, we
study this long-standing problem in terms of the nearly antiferromagnetic (AF)
Fermi liquid. We analyze the exact expression for the MR by including the
vertex corrections (VC's) to keep the conservation laws, and find the
approximate "scaling relation" $\Delta\rho/\rho \propto \xi_{AF}^4 /\rho^2$
($\xi_{AF}$ being the AF correlation length.) in the presence of AF
fluctuations. The factor $\xi_{AF}^4$, which comes from the VC's for the
current, gives the additional temperature dependence. By taking account of the
relation $R_H \propto \xi_{AF}^2$ [Kontani et al., PRB 59 (1999) 14723.], we
can naturally explain the modified Kohler's rule. In conclusion, based on the
Fermi liquid theory, the famous {\it seemingly} non-Fermi liquid behaviors of
the Hall coefficient and the MR in high-Tc cuprates are naturally understood on
an equal footing.
