  We discuss exact renormalization group (RG) in $R^2$-gravity using effective
average action formalism. The truncated evolution equation for such a theory on
De Sitter background leads to the system of nonperturbative RG equations for
cosmological and gravitational coupling constants. Approximate solution of
these RG equations shows the appearence of antiscreening and screening
behaviour of Newtonian coupling what depends on higher derivative coupling
constants.
