  We take account of the lowest order back reaction on the fluid and modify the
Kulsrud and Anderson equation $\partial_t{\cal E}_M= 2 \gamma {\cal E}_M$
obtained in the kinetic dynamo theory, where ${\cal E}_M$ is the energy density
of the magnetic field. Furthermore, we apply our present result to some
astrophysical stages where the magnetic field is expected to be amplified by
the dynamo mechanism.
