  Using the cosmological perturbation theory in terms of the delta-N formalism,
we find the simple formulation of the evolution of the curvature perturbation
in generalized gravity theories. Compared with the standard gravity theory, a
crucial difference appears in the end-boundary of the inflationary stage, which
is due to the non-ideal form of the energy momentum tensor that depends
explicitly on the curvature scalar. Recent study shows that
ultraviolet-complete quantum theory of gravity may be approximated by using a
generalized gravity action. Our paper may give an important step in
understanding the evolution of the curvature perturbation during inflation,
where the energy momentum tensor may not be given by the ideal form due to the
corrections from the fundamental theory.
