  Scaling symmetry of gl_n-type Drinfel'd-Sokolov hierarchy is investigated.
Applying similarity reduction to the hierarchy, one can obtain the Schlesinger
equation with (n+1) regular singularities. Especially in the case of n=3, the
hierarchy contains the three-wave resonant system and the similarity reduction
gives the generic case of the Painleve VI equation. We also discuss Weyl group
symmetry of the hierarchy.
