  A possible origin of the anomalous dip and bump in the primordial power
spectrum, which are reconstructed from WMAP data corresponding to the multipole
$\ell=100\sim 140$ by using the inversion method, is investigated as a
consequence of modification of scalar field dynamics in the inflation era.
Utilizing an analytic formula to handle higher order corrections to the
slow-roll approximation, we evaluate the relation between a detailed shape of
inflaton potential and a fine structure in the primordial power spectrum. We
conclude that it is unlikely to generate the observed dip and bump in the power
spectrum by adding any features in the inflaton potential. Though we can make a
fine enough shape in the power spectrum by controlling the feature of the
potential, the amplitude of the dip and bump becomes too small in that case.
