  We investigate f-electron charge susceptibility in a two-impurity Anderson
model on the basis of Wilson's numerical renormalization group method. The
f-electron charge susceptibility diverges logarithmically at the critical point
of this model when conduction-electron bands exhibit particle-hole symmetry.
Although the critical point disappears without the particle-hole symmetry, the
f-electron charge fluctuation is much more enhanced near the crossover regime
between the Kondo-Yosida singlet and intersite spin-singlet states than that in
the single-impurity case. This result shows that charge fluctuations are
enhanced owing to the competition between intersite and Kondo-Yosida spin
singlets. A possible scenario for the enhanced residual resistivity near the
region where the Kondo temperature becomes comparable with the N\'eel
temperatures under pressure in some heavy-fermion compounds is proposed.
