  The in-medium eta' mass and the eta'N interaction are investigated in an
effective theory based on the linear realization of the SU(3) chiral symmetry.
We find that a large part of the eta' mass is generated by the spontaneous
breaking of chiral symmetry through the U_A (1) anomaly. As a consequence of
this observation, the eta' mass is reduced in nuclear matter where chiral
symmetry is partially restored. In our model, the mass reduction is found to be
80MeV at the saturation density. Estimating the eta' N interaction based on the
same effective theory, we find that the eta' N interaction in the scalar
channel is attractive sufficiently to form a bound state in the eta' N system
with a several MeV binding energy. We discuss the origin of attraction by
emphasizing the special role of the sigma meson in the linear sigma model for
the mass generation of eta' and N.
