  The effect of the initial condition of inflation on the power spectra of
scalar and tensor perturbations is estimated assuming a slow-roll inflation
model. By defining a more general initial state in inflation particular
properties of the power spectrum such as oscillation can be revealed. The
behavior of the power spectrum is shown to exhibit a step-like variation with
respect to finite inflation length in cases of both radiation- and scalar
matter-dominated pre-inflation. The power spectrum is shown to oscillate in the
radiation-dominated case. The effects of such a power spectrum on the TT and TE
power spectra are examined for three typical slow-roll inflation models; a
small-field model, a large field model, and a hybrid model, considering both
pre-inflation models. It is found that the discrepancies between WMAP3 data and
the Lambda CDM model, such as suppression of the spectrum at l=2, may be
explained to a certain extent by the finite length of inflation for inflation
of close to 60 e-folds. The small-field inflation model with scalar
matter-dominated pre-inflation provides the best fit to the WMAP3 data among
the models considered. Relatively large changes in the angular TT power
spectrum occur in response to small changes in inflation length in the
radiation-dominated pre-inflation models, and half cases do not fit well with
the observed data. This behavior is considered to be attributable to the
oscillatory behavior of the power spectrum. The scalar matter-dominated case is
thus preferred to the radiation-dominated case of pre-inflation, independent of
the length of inflation.
