  We investigate the particle production of a scalar field $\chi$ coupled to an
inflaton field $\phi$ ($g^2\phi^2\chi^2/2$) in the {\it oscillating inflation}
model, which was recently proposed by Damour and Mukhanov. Although the
fluctuation of the $\phi$ field can be effectively enhanced during a stage of
the oscillating inflation, the maximum fluctuation is suppressed as the
critical value $\phi_c$ which indicates the scale of the core part of the
inflaton potential decreases, in taking into account the back reaction effect
of created particles. As for the $\chi$ particle production, we find that
larger values of the coupling constant $g$ are required to lead to an efficient
parametric resonance with the decrease of $\phi_c$, because an effective mass
of inflaton around the minimum of its potential becomes larger. However, it is
possible to generate the superheavy $\chi$ particle whose mass is greater than
$10^{14}$ GeV, which would result in an important consequence for the GUT
baryogenesis.
