  On the basis of an electronic model with separable attractive interaction,
the precursors at high temperature and strong coupling of the d-wave
superconducting state are investigated in the one-particle spectral function
$A({\bf k},\omega)$ and the total density of states $\rho(\omega)$, with the
use of the self-consistent $t$-matrix approximation. In the low-density region,
it is found that a gap-like structure at the Fermi level appears in $A({\bf
k},\omega)$ and $\rho(\omega)$ above the superconducting transition
temperature. It is shown that the pseudogap energy scale is determined by the
binding energy of the Cooper-pair.
