  We present CO luminosity evolution of both elliptical and spiral galaxies
based on a galactic wind model and a bulge-disk model, respectively. We have
found that the CO luminosity peaks around the epoch of galactic wind caused by
collective supernovae $\sim$ 0.85 Gyr after the birth of the elliptical with $M
= 2 \cdot 10^{12} M_\odot$ while $\sim$ 0.36 Gyr after the birth of the bulge
with $M = 2 \cdot 10^{11} M_\odot$. After these epochs, the CO luminosity
decreases abruptly because the majority of molecular gas was expelled from the
galaxy system as the wind. Taking account of typical masses of elliptical
galaxies and bulges of spiral galaxies, we suggest that CO emission can be
hardly detected from galaxies with redshift $z \sim 1 - 4$ unless some
amplification either by galaxy mergers and/or by gravitational lensing is
working. Therefore, our study explains reasonably why CO emission was detected
from the high-redshift quasar BR 1202$-$0725 at $z =4.7$ while not detected
from the powerful radio galaxies with $1 < z < 4$.
