  For a diagram automorphism of an affine Kac-Moody algebra such that the
folded diagram is still an affine Dynkin diagram, we show that the associated
Drinfeld-Sokolov hierarchy also admits an induced automorphism. Then we show
how to obtain the Drinfeld-Sokolov hierarchy associated to the affine Kac-Moody
algebra that corresponds to the folded Dynkin diagram from the invariant
sub-hierarchy of the original Drinfeld-Sokolov hierarchy.
