  We numerically investigate density perturbations generated in the smooth
hybrid new inflation model, a kind of double inflation model that is designed
to reproduce the running spectral index suggested by the WMAP results. We
confirm that this model provides the running spectral index within 1sigma range
of the three year WMAP result. In addition, we find a sharp and strong peak on
the spectrum of primordial curvature perturbation at small scales. This
originates from amplification of fluctuation in the first inflaton fields due
to parametric resonance, which takes place in the oscillatory phase between two
inflationary regime. Formation probability of primordial black holes (PBHs) is
discussed as a consequence of such peak.
