  We study the mass spectra of excited baryons with the use of the lattice QCD
simulations. We focus our attention on the problem of the level ordering
between the positive-parity excited state N'(1440) (the Roper resonance) and
the negative-parity excited state N^*(1535). Nearly perfect parity projection
is accomplished by combining the quark propagators with periodic and
anti-periodic boundary conditions in the temporal direction. Then we extract
the spectral functions from the lattice data by utilizing the maximum entropy
method. We observe that the masses of the N' and N^* states are close for wide
range of the quark masses (M_pi=0.61-1.22 GeV), which is in contrast to the
phenomenological prediction of the quark models. The role of the Wilson
doublers in the baryonic spectral functions is also studied.
