  We study theoretically the spin transfer effect on a domain wall in
disordered weak ferromagnets. We have identified the adiabatic condition for
the disordered case as $\lambda \gg \lambda_{\rm D}\equiv \sqrt{{\hbar
D}/{\spol}}$, where $D$ and $\spol$ are the diffusion constant and the spin
splitting energy due to the $s$-$d$ type exchange interaction, respectively,
and found out that perfect spin-transfer effect occurs even in weak
ferromagnets as long as this condition is satisfied. The effective $\beta$ term
arising from the force turns out to govern the wall dynamics, and therefore,
the wall motion can be as efficient as in strong ferromagnets even if $\spol$
is small.
