  We investigate photoproduction of the scalar mesona off the nucleon, using
the effective Lagrangians and the Regge approach. We first study $f_0(980)$
photoproduction, replacing the Feynman propagator with the Regge ones for the
$\rho$-meson exchange in the $t$-channel. The model parameters are fixed by
reproducing the experimental data on the differential cross section. We then
apply the same method to $f_0(500)$ or $\sigma$ photoproduction with the same
parameters for the Regge propagator. Since the threshold energy of the
$f_0(500)$ production is rather low, $N^*$ resonances, which can decay into the
nucleon and two pions in the isoscalar and scalar state, can come into play in
the $s$-channel. To examine the effects of the $N^*$ resonances, we set up two
models to look into the respective contribution of the $N^*$ resonances. We
find that in particular $N^*(1440)$ and $N^*(1680)$ play important roles in
$f_0(500)$ photoproduction. We discuss the physical implications of the present
results.
