  We consider several integrable systems from a standpoint of the SL(2,R)
invariant gauge theory. In the Drinfeld-Sokorov gauge, we get a one parameter
family of nonlinear equations from zero curvature conditions. For each value of
the parameter the equation is described by weak Lax equations. It is
transformed to a set of coupled equations which pass the Painlev\'{e} test and
are integrable for any integer values of the parameter. Performing successive
gauge transformations (the Miura transformations) on the system of equations we
obtain a series of nonlinear equations.
