  We investigate anisotropic charge fluctuations in the two-dimensional Hubbard
model at half filling. By the quantum Monte Carlo method, we calculate a
momentum-resolved charge compressibility $\kappa (\bm{k}) = {d < n(\bm{k})
>}/{d \mu}$, which shows effects of an infinitesimal doping. At the temperature
$T \sim {t^2}/{U}$, $\kappa (\bm{k})$ shows peak structure at the $(\pm
\pi/2,\pm \pi/2)$ points along the $|k_x| + |k_y| = \pi$ line. A similar peak
structure is reproduced in the mean-filed calculation for the d-wave pairing
state or the staggered flux state.
