  We investigate the superconducting (SC) state in two-dimensional extended
Hubbard model at a quarter-filling with the on-site repulsive interaction ($U$)
and the nearest-neighbor one ($V$), which lead to the spin fluctuation and the
charge fluctuation, respectively. The effect of the charge fluctuation on the
onset of the SC state is calculated by estimating the pairing interaction
within the random phase approximation. Solving the linearized Eliashberg
equation with the anomalous self-energy as the function of both momentum and
frequency, we examined the singlet SC state on the plane of $U$ and $V$ with
the fixed temperature. We found a novel result that the SC state with the
$d_{xy}$ symmetry retains for most parameters of $U$ and $V$, although the
pairing interaction changes the sign from repulsive one into attractive one
with increasing $V$. The reentrant transition as the function of temperature
occurs close to the onset of the SC state.

Superconductivity