  The exact renormalization group is applied to a nonlinear diffusion equation
with a discontinuous diffusion coefficient. The generating functional of the
solution for the initial-value problem of nonlinear diffusion equations is
first introduced, and next a new regularization scheme is presented. It is
shown that the renormalization of an action functional in the generating
functional leads to an anomalous diffusion exponent in full order of the
perturbation series with respect to a nonlinearity.
