  Based on the radiation hydrodynamical model for the black hole(BH)
growth,incorporated with the chemical evolution of the early-type host galaxy,
we construct the coevolution model of a QSO BH and the host galaxy. As a
result, it is found that after a galactic wind epoch,the luminosity is shifted
from the host-dominant phase to the AGN-dominant phase (QSO phase) in the
timescale of a few $10^{8}$ years.The former phase corresponds to the early
stage of growing BH, and can be regarded as a ``proto-QSO'' phase. It has
observable characteristic properties (detail inthis paper).By comparing these
predictions with recent observations, radio galaxies are a possible candidate
for proto-QSOs.Also, it is anticipated that the proto-QSO phase is preceded by
an optically thick phase, which may correspond to ULIRGs.In this phase, $M_{\rm
BH}/M_{\rm bulge}$ is predicted to be much less than $10^{-3}$ and grow with
metallicity.Moreover, as precursors of ULIRGs, optically-thin star-forming
galaxies are predicted. These may be in the assembly phase of Lyman break
galaxies (LBGs) or Ly$\alpha$ emitters.
