  In this paper we study the effects of the strong coupling superconductivity
on the normal state electronic structure. We point out that the pseudogap
phenomena in High-T_c cuprates are naturally explained as a precursor of the
strong coupling superconductivity.
  We expand the reciprocal of the T-matrix with respect to the momentum and the
frequency, and we discuss the properties of the expansion parameters. We
estimate these parameters and carry out the calculations for the single
particle self-energy using the T-matrix and the self-consistent T-matrix
approximations, respectively.
  We show that the superconducting fluctuations, which are strongly diffusive
within the conventional weak coupling theory, become propagative and have the
character of the pre-formed pairs in the strong coupling case.
  The spectral weight and the density of states show the gap-like features by
the effects of the resonances with the thermally excited weakly-damped
pre-formed pairs.
  The spectral weight at the Fermi energy is strongly suppressed.
  This suppression starts at the mean field critical temperature $T_{MF}$ and
the actual critical temperature T_c is strongly reduced owing to the
fluctuations.
  These features properly explain to the pseudogap phenomena in High-T_c
cuprates.
