  Magnon drag effect induced by an applied electric field in ferromagnetic
metals is theoretically studied by a microscopic calculation of the force on
magnons arising from magnon emission/absorption and scattering due to driven
electrons. It is shown that magnon scattering contribution dominates over the
emission/absorption one in a wide temperature regime in good metals with long
elastic lifetime $\taue$, as the latter has a relative suppression factor of
$(\Deltasd\taue)^{-2}$ due to the electron spin flip by the magnon, where
$\Deltasd$ is the $sd$ exchange interaction energy. Spin-transfer efficiency is
discussed including the magnon drag effect.
