  The deviation of the experimental value of $R_b \equiv \Gamma_b/\Gamma_h$
from the standard-model prediction can be naturally explained in the extended
technicolor scenario.The diagonal extended technicolor gauge boson which
flavor-diagonally couples with both the ordinary fermions and the
techni-fermions plays an important role in order to have the appropriate
radiative correction to the $Zbb$ vertex. But since the diagonal extended
technicolor gauge boson gives too large positive contribution to the $T$
parameter, we need some new mechanisms which generate negative contribution to
the $T$ parameter.
