  We discuss the studies on structure functions at the possible future RCNP
facility. At this stage, an electron-proton or proton-proton collider with
sqrt{s}=5 - 10 GeV is considered. We explain large-x physics, nuclear
modification of sea-quark and gluon distributions, and tensor spin structure
function as the interesting topics at the facility. The large-x parton
distributions are important for finding new physics beyond QCD in anomalous
events such as the CDF jet data. The nuclear parton distributions are valuable
in detecting a quark-gluon signature in heavy-ion reactions. The tensor
structure function b_1 is a new field of high-energy spin physics. Considering
these physics possibilities, we believe that the possible RCNP facility is
important for the hadron-structure community.
