  Finite-volume effects for the nucleon chiral partners are studied within the
framework of the parity-doublet model. Our model includes the vacuum energy
shift for nucleons, which is the Casimir effect. We find that for the
antiperiodic boundary the finite-volume effect leads to chiral symmetry
restoration, and the masses of the nucleon parity doublets degenerate. For the
periodic boundary, the chiral symmetry breaking is enhanced, and the masses of
the nucleons also increase. We also discuss the finite-temperature effect and
the dependence on the number of compactified spatial dimensions.
