  We theoretically investigate the origin of the resonant x-ray scattering
(RXS) signal near the Ce $L_{III}$ absorption edge in the quadrupolar ordering
phase of CeB$_6$, considering the intersite interaction between the $\Gamma_8$
states in the initial state. The anisotropic charge distribution of the $4f$
states modulates the $5d$ states through the intra-atomic Coulomb interaction
and thereby generates a large RXS superlattice intensity. The temperature and
magnetic field dependence indicates that the induced dipolar and octupolar
orders have little influence on the RXS spectra, in good agreement with the
recent experiment.
