  We investigate a resonant particle production of a scalar field $\chi$
coupled non-minimally to a spacetime curvature $R$ ($\xi R \chi^2$) as well as
to an inflaton field $\phi$ ($g^2\phi^2\chi^2$). In the case of $g < 3 \times
10^{-4}$, $\xi$ effect assists $g$-resonance in certain parameter regimes.
However, for $g > 3 \times 10^{-4}$, $g$-resonance is not enhanced by $\xi$
effect because of $\xi$ suppression effect as well as a back reaction effect.
If $\xi \approx -4$, the maximal fluctuation of produced $\chi$-particle is
$\sqrt{< \chi^2 >}_{max} \approx 2 \times 10^{17}$ GeV for $g < 1 \times
10^{-5}$, which is larger than the minimally coupled case with $g \approx 1
\times 10^{-3}$.
