  A possibility of the electronic origin of the high-temperature
superconductivity in cuprates is probed with the quantum Monte Carlo method by
revisiting the three-band Hubbard model comprising Cu$3d_{x^2-y^2}$ and
O$2p_\sigma$ orbitals. The $d_{x^2-y^2}$ pairing correlation is found to turn
into an increasing function of the repulsion $U_d$ within the $d$ orbitals or
the $d$-$p$ level off-set $\Delta \varepsilon$, where the correlation grows
with the system size. % and is long-ranged as also seen from a real-space
analysis. We have detected this in both the charge-transfer and Mott-Hubbard
regimes upon entering the strong-correlation region ($U_d$ or $\Delta
\varepsilon >$ bare band width).
